You've finished your manuscript. You've read it through twice, maybe three times, tightening a scene here and cutting a subplot there. Then it comes back from a beta reader covered in grammar notes. Not plot notes. Not character notes. Grammar notes. What's actually wrong?
If you've been there, you're not alone. It's one of the most common moments in a writer's life: you know the story works, but something on the sentence level keeps pulling readers out of it. This guide clears up which grammar mistakes actually matter to authors, why they matter, and exactly how to catch and fix them before you submit to an agent, send your manuscript to a publisher, or hit publish yourself.
By the end, you'll know the most common grammar mistakes that show up in manuscripts, the difference between a genuine mistake and a deliberate style choice, and how to run a proper self-edit pass that catches the errors most likely to cost you a reader's trust or an agent's attention.
This isn't a school grammar refresher, and it isn't going to walk you through what a noun or a verb is. You already know that. What you're probably less sure of is which of these rules genuinely matter to how your writing is judged, and which ones are the kind of pedantic nitpick that no working editor actually cares about. That distinction is the whole point of this guide, and it's the difference between spending your remaining editing time wisely and spending it chasing rules that don't move the needle.
Let's start with the mistakes that show up most often.
What Counts as a Grammar Mistake (vs a Style Choice)?
Before you go hunting for errors, it helps to know what you're actually hunting for. A grammar mistake breaks an established rule of the language itself. A style choice bends a convention on purpose, for voice or rhythm.
Think of it like a fence around a field. Grammar rules are the fence. Style is how you choose to walk within it. You can wander close to the edge, cut across at an angle, even sit down in the middle of the grass if that's the effect you're after. What you can't do, at least not without readers noticing, is walk straight through the fence and pretend it isn't there.
This distinction matters because a lot of writers either over-correct, sanding every fragment and every deliberate repetition out of their prose until it reads like a textbook, or under-correct, waving away genuine errors as "just my voice." Neither serves the story. The dictionary and any decent style guide will tell you where the fence actually sits: what counts as a genuine agreement error, a punctuation rule, a tense inconsistency, versus what's a legitimate stylistic device.
Expert tip: Learn the rule properly before you decide to break it on purpose. Readers and agents can tell the difference between a deliberate fragment and a mistake.
Here's a quick way to see the difference in action. A genuine grammar mistake might look like: "Neither of the twins were telling the truth." That's a subject-verb agreement error; "neither" is singular, so it should be "was." A stylistic fragment, on the other hand, might look like: "She ran. Didn't look back. Couldn't." That's not broken grammar. That's a writer choosing short, clipped sentences to mirror urgency. One is an accident. The other is a decision.
The confusion usually comes from the fact that both examples can look similarly "incorrect" on the page to someone skimming for errors with a checklist rather than reading with intent. A grammar-checking tool, in particular, will often flag both the same way, because software can't tell you why a sentence is short, only that it is. That's precisely why this guide focuses on teaching you to recognise the underlying rule rather than just handing you a list of red flags to avoid. Once you understand why "neither... were" is wrong, you'll also understand why "She ran. Didn't look back." isn't, even though neither one is a complete, textbook sentence.
The Most Common Grammar Mistakes Writers Make
These are the errors that turn up again and again in manuscripts, across genres, from first-time writers and experienced novelists alike. Some are small and forgivable in isolation but damaging in volume. Others are the kind of error that, on page one, tells an agent everything they need to know about how carefully a manuscript has been prepared. Each one below comes with a wrong example and a corrected version, so you can spot the pattern in your own pages.
1. Homophone Confusion
Their, there, they're. Its, it's. Your, you're. Then, than. These words sound identical or nearly identical when read aloud, which is exactly why they slip past a writer working quickly, and exactly why a spellchecker often won't catch them; each version is a correctly spelled word, just the wrong one.
Wrong: "The dog wagged it's tail happily." Right: "The dog wagged its tail happily."
Wrong: "Their coming over later to discuss the manuscript." Right: "They're coming over later to discuss the manuscript."
Expert tip: Run a single find-and-check pass for its/it's and their/there/they're before anything else. These account for a disproportionate share of manuscript errors, and they're also some of the fastest to fix once you know where to look.
This mistake shows up everywhere, regardless of genre. In fiction, it tends to hide inside fast-moving action beats, where a writer's attention is on what happens next rather than which homophone just went down on the page. In memoir, it often slips into reflective passages written quickly, in one long emotional pass, before a second read. In nonfiction, it's just as likely to appear in a rushed introduction or conclusion, the two sections most often written last and proofread least. Genre doesn't protect you from this one. Speed is the real culprit, so slowing down for a single dedicated pass matters more than which kind of book you're writing.
2. Apostrophe Misuse
Apostrophes trip people up in possessives and plurals alike. The confusion usually comes down to one question: is this word showing ownership, or is it simply more than one of something?
Wrong: "The authors book was finally ready for submission." Right: "The author's book was finally ready for submission."
Wrong: "Both author's agreed to the new deadline." Right: "Both authors agreed to the new deadline." (No apostrophe needed. There's no ownership here, just two authors.)
Wrong: "The three book's on the shelf belonged to her grandmother." Right: "The three books on the shelf belonged to her grandmother."
Expert tip: If you can replace the word with "belonging to," you need an apostrophe. If you're just talking about more than one, you don't.
Plural possessives cause a particular kind of confusion. "The authors' royalties" (more than one author, each with royalties) is different from "the author's royalties" (one author). Get this wrong in a nonfiction manuscript discussing multiple contributors, and the meaning genuinely shifts, not just the formatting. It's one of the few grammar mistakes on this list that can actually change what a sentence means rather than just how polished it looks.
3. Comma Splices and Run-on Sentences
A comma splice happens when you join two complete sentences with nothing but a comma. A run-on sentence goes a step further and drops the punctuation entirely. Both are common in fast-drafted fiction, especially in scenes with a lot of momentum, where a writer's instinct is to keep the sentence moving rather than break it.
Wrong: "She opened the door, he was gone." Right: "She opened the door. He was gone." Or: "She opened the door, and he was gone."
Wrong: "The rain hadn't stopped for days the fields had turned to mud." Right: "The rain hadn't stopped for days, and the fields had turned to mud."
Expert tip: Read the sentence aloud. If you'd naturally pause with a full stop, use one, or add a conjunction. Your ear will catch what your eye skips over.
Comma splices are especially common in thriller and suspense writing, where the whole point of a scene is to keep the reader's pulse up, and short, breathless sentences feel like the right tool for that job. The problem is that a genuine comma splice doesn't read as breathless. It reads as unfinished. There's a real difference between a deliberate short sentence used for pace and two full sentences accidentally glued together with a comma because the writer never slowed down to punctuate properly. The fix, more often than not, is simply choosing: full stop, or conjunction. Rarely does the sentence lose any urgency for it.
4. Subject-Verb Agreement
This one gets slippery with collective nouns and long subject phrases, where a nearby noun tricks the ear into agreeing with the wrong word.
Wrong: "The list of names were long." Right: "The list of names was long." (The subject is "list," singular, not "names.")
Wrong: "The team of editors are reviewing the draft this week." — This is actually a case where UK and US usage genuinely differ, which we'll come back to shortly. In UK English, "the team are reviewing" is broadly acceptable because a team is treated as a group of individuals; in US English, "the team is reviewing" is the standard form.
Expert tip: Strip the sentence down to its bare subject and verb to check agreement, ignoring everything in between. "The list... was long," not "names... were long."
Long, layered sentences make this mistake far more likely, simply because there's more distance between the true subject and its verb, and more nouns along the way competing for the ear's attention. It's rarely a sign that a writer doesn't understand agreement in principle; it's usually a sign the sentence has grown complex enough that even a careful writer loses track partway through. If you notice a particular sentence has three or four clauses stacked up before the verb finally arrives, that's exactly the kind of sentence worth checking twice.
5. Inconsistent Verb Tense
Tense slips are one of the sneakiest errors to catch in your own work, because you're inside the scene as you write it, and your brain fills in continuity your reader doesn't have. The most common place this happens is around flashbacks and scene breaks, where a writer drifts from past tense into present tense, or back again, without meaning to.
Wrong: "She remembered the summer they spent at the coast. He builds a fire on the beach, and they watch it burn down to nothing." Right: "She remembered the summer they spent at the coast. He'd built a fire on the beach, and they'd watched it burn down to nothing."
Expert tip: Keep verb tense consistent within a scene. Flashbacks are the most common place tense slips in, so give them a dedicated read-through of their own.
Memoir writers run into a particular version of this problem: writing about the past in past tense feels natural, but the moment a reflective, present-day observation gets folded into the same paragraph, the tense can start sliding without the writer noticing, because both feel emotionally "true" in the moment of writing. Fiction writers hit the same wall in dual-timeline structures, where one thread runs in past tense and another in present, and a scene break doesn't always make the switch as obvious to a reader as it felt to the writer. Nonfiction has its own version too, when a writer moves from describing a historical event to describing its ongoing relevance without adjusting the verbs to match. In every case, the fix is the same: check each scene or section on its own terms, not just against the paragraph before it.
6. Dangling and Misplaced Modifiers
A dangling modifier is a descriptive phrase that doesn't clearly attach to the noun it's meant to describe, which can create meaning that's confusing or, worse, unintentionally comic.
Wrong: "Running late, the bus was missed." (This implies the bus was running late, not the person.) Right: "Running late, she missed the bus."
Wrong: "After finishing the manuscript, the coffee had gone cold." Right: "After finishing the manuscript, she noticed the coffee had gone cold."
Expert tip: Ask "who or what is doing this action?" and make sure that word sits right next to the modifier. If it doesn't, the sentence needs restructuring, not just a comma fix.
These are especially easy to miss in your own writing because you know what you meant. A reader doesn't have that advantage; they only have the words on the page, in the order you put them. That gap between intended meaning and literal meaning is exactly what a fresh pair of eyes, whether a beta reader or a professional editor, tends to catch far faster than the writer who's been staring at the same paragraph for weeks.
7. Dialogue Punctuation Mistakes
Dialogue punctuation is a formatting convention as much as a grammar rule, but it's one of the more visible signs of an under-edited manuscript, because agents and readers see it on nearly every page. The most common error is using a full stop instead of a comma before a dialogue tag.
Wrong: "I'm leaving." She said. Right: "I'm leaving," she said.
Wrong: "Where are you going," he asked? Right: "Where are you going?" he asked.
Expert tip: Use a comma before a dialogue tag ("he said," "she asked") and a full stop only when there's no tag at all: "I'm leaving." She walked out and didn't look back. That second sentence is a separate action, not a tag, so it takes its own full stop.
There's a second, related error worth flagging here: capitalisation after a tag. If the dialogue tag comes first, the quoted speech that follows still starts with a capital letter, as any new sentence would. But if a tag interrupts a single sentence of dialogue, the second half continues in lower case. Wrong: "I don't know," she said, "What you expect from me." Right: "I don't know," she said, "what you expect from me." The comma after "said" signals that the sentence is continuing, not starting fresh.
Dialogue-heavy scenes carry a lot of a story's momentum, especially around a turning point in the plot, where pacing and clarity matter most and a punctuation slip is most likely to break the reader's focus at exactly the wrong moment.
Why Grammar Mistakes Matter for Authors Specifically
Here's the question most writers are actually asking, underneath all the specific rules: will grammar mistakes get my manuscript rejected?
The honest answer is nuanced, and it's worth sitting with rather than skating past. Agents and editors often read only the first few pages of a submission before deciding whether to keep going. If those pages contain repeated grammar errors, they can read as a lack of polish before the story has even had a chance to prove itself. It's not that any single its/it's slip will sink a manuscript. It's that a pattern of small errors erodes a reader's trust in the narrator's voice and pulls their attention away from the story you're trying to tell them.
Think about it from the other side of the desk. An agent reading a submission is looking for reasons to keep reading, but they're also looking for reasons to stop, because they have a stack of other manuscripts waiting. A page riddled with comma splices and inconsistent tense gives them an easy, low-effort reason to put yours down. A clean page doesn't guarantee they'll fall in love with your story, but it removes one of the easiest excuses to reject it.
There's also a subtler cost that has nothing to do with agents or gatekeepers at all: reader trust. If a reader hits three or four glaring errors in the first chapter, they start reading differently. They stop trusting the narrator. They start looking for more mistakes instead of following the story. That shift in attention is exactly what good prose is supposed to prevent.
Expert tip: A clean manuscript won't guarantee acceptance, but a sloppy one gives an agent an easy reason to stop reading.
The good news is that grammar mistakes are, on the whole, some of the most fixable problems in a manuscript. Plot holes take rewrites. Weak character motivation takes rethinking. A comma splice takes a comma.
It's worth separating two things that often get conflated in a writer's mind: manuscript quality and manuscript readiness. Grammar mistakes rarely tell you anything about whether your story is good. Plenty of brilliant, publishable stories arrive in early drafts full of homophone slips and inconsistent tense, because that's simply what a first or second draft looks like. What grammar mistakes tell an agent, editor, or reader is whether the manuscript in front of them right now is ready to be judged. Submitting before that self-edit pass is done isn't a reflection of your talent. It's just premature, and it costs you a fair reading of work that might otherwise land.
Grammar Mistakes vs Style Choices
Not every "rule" you learned in school is actually a hard rule in fiction. Sentence fragments in dialogue, split infinitives, and starting a sentence with "and" or "but" are often deliberate style choices rather than errors, and plenty of published, critically respected books use all three.
The test is simple: was this done on purpose, for effect, and does it read clearly? If the answer to both is yes, it's style, not a mistake.
Take fragments in dialogue. Real speech is full of them. Nobody talks in complete, grammatically tidy sentences when they're upset, distracted, or interrupted, so forcing full sentences into dialogue can actually make it read less naturally, not more. Compare "I don't know what to say to you." with "I don't. Know what to say." The second version, used deliberately in the right emotional beat, does something the first can't.
The same goes for genre. What reads as a stylistic fragment in literary fiction or memoir might genuinely be a mistake in a piece of formal nonfiction where clarity and precision carry more weight than rhythm. Context decides which side of the fence you're on, which is exactly why it pays to know the rule first. You can't make a confident stylistic choice to break a rule you don't actually understand.
Split infinitives are another good example of a "rule" that's softer than most writers assume. "To boldly go" splits "to go" with "boldly," and generations of schoolchildren were taught this was wrong. In practice, most modern style guides accept it where the alternative sounds stiff or changes emphasis awkwardly. "To go boldly" simply doesn't carry the same weight. The rule exists, but it's flexible, and treating it as an absolute is exactly the kind of over-correction that can flatten a writer's natural voice.
The same applies to starting a sentence with "and" or "but." It's taught as an error in school largely to stop young writers from producing strings of disconnected fragments, not because the construction is genuinely ungrammatical. Used deliberately, in moderation, it can create emphasis a full conjunction in the middle of a sentence can't match. Used constantly, without intent, it starts to read as a tic rather than a technique. The line between the two comes down to frequency and purpose, not the rule itself.
Expert tip: Learn the rule properly before you decide to break it on purpose. Readers and agents can tell the difference between a deliberate fragment and a mistake.
UK English vs US English: What to Watch For
If you're a UK-based author submitting to UK agents and publishers, this section matters more than it might seem at first glance. The core grammar rules are the same across both varieties of English, but the differences that do exist are exactly the kind that trip up a manuscript trying to look polished and consistent.
Spelling. UK English favours -ise endings over -ize: organise, realise, recognise, rather than organize, realize, recognize. It also keeps the "u" in words like colour and favourite, where American spelling drops it. These aren't stylistic preferences; they're the standard convention for UK publishing, and mixing the two within a single manuscript reads as inconsistent rather than intentional.
Quotation marks. UK convention often favours single quotation marks for dialogue, with double quotes reserved for a quote within a quote, though house style genuinely does vary from one publisher's imprint to another, so it's worth checking submission guidelines directly rather than assuming.
Collective nouns. This is one of the more interesting genuine grammar differences. UK English often treats collective nouns as plural: "the team is reviewing the manuscript," "the band are on tour." US English typically treats the same nouns as singular: "the team is reviewing," "the band is on tour." Neither is wrong; they're simply different conventions, and consistency within your manuscript is what matters.
Dates and numbers. UK English uses day-month-year formatting (2 September 2026, not September 2, 2026), and British convention differs from American convention in how commas and full stops are used in large numbers.
Expert tip: Decide once whether you're writing in UK or US English and set your word processor's language and spellcheck to match for the whole manuscript. Trying to switch mid-draft is where most of these inconsistencies creep in.
It's also worth being transparent with yourself that these conventions vary by publisher house style, so once you have a specific submission target, check their guidelines directly rather than relying on a general rule.
There's a further layer worth knowing about, even if it rarely comes up in day-to-day drafting: punctuation placement around quotation marks. UK convention typically places a full stop or comma outside the closing quotation mark unless it's part of the quoted material itself, while American convention tends to place it inside regardless. It's a small detail, and one most readers will never consciously notice, but it's exactly the kind of small detail that a careful copyeditor or agent will notice, because consistency across hundreds of instances of dialogue and quotation is one of the clearest tells of a professionally prepared manuscript versus one that hasn't had a dedicated pass.
None of this means you need to become an expert in comparative linguistics before you submit. It means picking one convention, applying it consistently, and trusting that consistency matters more than perfection on any single instance.
Mistake vs Quick Fix Comparison Table
Here's a scannable reference you can return to while self-editing, pairing each common mistake with its fix and why it actually matters to a reader or an agent.
Mistake | Wrong example | Quick fix | Why it matters |
its / it's | The dog wagged its tail. | Use it's only for "it is" or "it has." | One of the most flagged errors by agents and editors. |
Comma splice | She opened the door; he was gone. | Split into two sentences or add a conjunction. | Muddles pacing and can confuse cause and effect. |
Dangling modifier | Running late, the bus was missed. | Attach the modifier to the person doing the action. | Creates unintentionally comic or confusing meaning. |
Subject-verb agreement | The list of names was long. | Match the verb to the true subject, not the nearest noun. | A quiet but frequent slip in longer sentences. |
Dialogue punctuation | "I'm leaving." She said. | Use a comma before a dialogue tag, not a full stop. | Standard formatting expected by agents and readers. |
Self-Editing Checklist Before You Submit
Run through this before you send your manuscript to an agent, a publisher, or straight to self-publishing. Treat it as a dedicated pass in its own right, separate from your plot or character edits, rather than something you try to catch as a side effect of reading for story:
Read your dialogue aloud to catch comma splices and missing tags.
Search for its/it's and their/there/they're and check every single instance.
Check verb tense within each scene, especially around flashbacks.
Confirm your word processor's language is set to UK English throughout.
Read for dangling modifiers by checking what the opening phrase of each sentence actually attaches to.
Run a grammar-checking tool pass, then review its suggestions rather than accepting them all automatically.
Do a final read-through focused purely on consistency in dialogue punctuation and tag formatting.
This isn't a one-hour task, and it isn't meant to be. Give yourself real time between passes; you'll catch far more on a fresh read than you will trying to power through all seven steps back to back.
Tools and When to Hire a Professional Proofreader
Self-editing software has a real place in this process, but it works best as a first pass, not a final judge. A grammar-checking tool is good at flagging patterns: repeated homophone slips, missing commas, obvious agreement errors. What it consistently misses is context, especially in dialogue and stylistic fragments, where the "rule" it's flagging is exactly the choice you made on purpose. Accept its suggestions selectively, not automatically.
Expert tip: Use a grammar tool as a first pass, not a final judge. It flags patterns but misses context, especially in dialogue and stylistic fragments.
There's also a real difference between what software catches and what a trained human eye catches. Idiomatic dialogue, voice-driven prose, and the kind of deliberate rule-breaking discussed earlier are exactly where software falls short and a professional proofreader earns their keep. If your manuscript is voice-driven or dialogue-heavy, this is usually the point where a second, human pass on your grammar pays for itself. Beyond a straight proofread, a full editing service can also catch structural and consistency issues a grammar pass alone won't touch, from pacing to point-of-view slips across chapters.
A useful way to think about the difference: a proofread is largely about correctness, catching the kind of errors covered throughout this guide, page by page, right up to the final version before publication. An edit goes further, looking at whether the writing works as a whole, whether the pacing holds, whether a character's voice stays consistent across three hundred pages. Most manuscripts benefit from both at different stages, and knowing which one you actually need can save you time and money rather than paying for the wrong kind of pass at the wrong point in your process.
Expert tip: A human proofreader will still catch what software misses, especially with idiomatic dialogue and voice-driven prose.
Grammar is only one layer of getting a manuscript submission-ready, of course. Once the sentence-level work is done, most authors still have questions about what a literary agent is actually looking for beyond clean prose, and how house style and an imprint's own conventions might shape final formatting decisions later in the process.
Thinking About What Comes After the Grammar Pass?
Once your manuscript is grammatically sound, the next questions tend to be about getting it in front of readers. If you're weighing up whether to write the book yourself or bring in support, a fiction ghostwriting service can help shape a novel from concept to finished draft, while a non-fiction ghostwriting service does the same for books built around expertise or research rather than plot. Memoirists often have a related but distinct need, and an autobiography writing service is built specifically around turning a life story into a readable narrative arc. If your book is closer to practical guidance than narrative, a self-help book writing service focuses on structuring advice so it lands clearly with readers. And if you'd rather write it entirely yourself but want a broader hand across the whole project, a general creative writing service or ghostwriting service can flex to whatever stage you're at.
Grammar and structure aside, plenty of manuscripts still need to find their format. Authors publishing digitally often have specific formatting needs covered by an e-book writing service, while print-bound manuscripts need dedicated book formatting to be submission- or publication-ready. Once the words themselves are settled, most authors turn their attention to how the book looks: book design services shape everything from interior layout to typesetting, and designing a book cover is very much its own skill, distinct from anything covered in this guide. If you're still deciding what kind of book you're even writing, it's worth reading about the different types of books before you commit to a structure.
None of this happens in a vacuum, either. Once a manuscript is clean, formatted and designed, most authors are thinking about how readers will actually find it, which is where book marketing services come in, and about the wider process of getting a finished book into the world through dedicated book publishing services. If any of this feels like a lot to take on alone, UK Print and Publish works with authors across every one of these stages, from the first grammar pass through to a finished, published book. And if you're plotting a pivotal scene as you revise, it's worth reading about how to build a genuine turning point in a story, since pacing and grammar tend to matter most in exactly those high-tension pages.
Common Mistakes
Here's a quick recap of the errors covered in this guide, followed by the questions authors ask most often once they start their own self-edit pass.
Confusing its and it's, or their, there, and they're. These homophones are the single most flagged error across manuscripts, largely because a spellchecker won't catch a correctly spelled wrong word. "Its" shows ownership ("the cat licked its paw"), while "it's" is always short for "it is" or "it has." "Their" shows ownership, "there" points to a place, and "they're" is short for "they are." Because each version passes a basic spellcheck, this mistake tends to survive multiple read-throughs unless you check for it specifically rather than hoping you'll spot it by eye.
Comma splices join two full sentences without a conjunction. Common in fast-paced or high-momentum scenes, where the instinct is to keep the sentence moving rather than break it. A comma splice happens when two sentences that could each stand alone get joined with just a comma, as in "She grabbed her coat, the rain hadn't let up." The fix is usually a full stop, a semicolon, or a conjunction like "and" or "but," and none of those options need to slow the pacing down as much as a writer often fears.
Apostrophe errors in possessives and plurals. Usually comes down to confusing "more than one" with "belonging to." A simple plural, like "three chapters," never takes an apostrophe. A possessive, like "the chapter's opening line," does. Where it gets trickier is plural possessives: "the editors' notes" (several editors, each with notes) versus "the editor's notes" (one editor). Getting this wrong doesn't just look untidy; in the wrong context, it can genuinely change how many people the sentence is talking about.
Inconsistent tense across a scene or chapter. Most common around flashbacks, where the narrative shifts time without the verbs shifting with it. A scene set firmly in the past should generally stay in past tense throughout, and a flashback within that scene usually needs a shift into past perfect ("she had walked," not "she walks") to signal clearly that the timeline has moved. Readers rarely notice tense when it's handled correctly; they notice almost immediately when it isn't, because it disrupts their sense of when, exactly, they are in the story.
Dialogue tags punctuated with a full stop instead of a comma. One of the most visible formatting slips on a submission page, because dialogue appears on nearly every page of a novel or memoir. The rule is straightforward once it's pointed out: a comma goes before a tag like "she said" or "he asked," and a full stop is reserved for moments when the spoken line is followed by a separate action rather than a tag, such as "I'm leaving." She reached for the door.
Mixing UK and US spelling conventions within the same manuscript. Easy to do if your word processor's language setting doesn't match your intended convention, especially if you've drafted using different devices or software over time. A manuscript that switches between "organise" and "organize," or "colour" and "color," within the same chapter reads as inconsistent rather than deliberate, even though each individual word is spelled correctly on its own terms. Setting your language preference once, at the start of a project, is the simplest way to avoid having to hunt these down later.
Conclusion
Most grammar mistakes are easy to catch once you know exactly what to look for. Homophones, comma splices, apostrophes, tense slips, modifiers, and dialogue punctuation account for the vast majority of what shows up in manuscripts, and every one of them is fixable with a focused read-through rather than a full rewrite.
The bigger takeaway is this: know the difference between a genuine mistake and a deliberate style choice, check systematically for the most common errors, confirm you're consistent in your English convention from page one to the last, and run a proper self-edit pass before anyone else sees your work.
Start with the self-editing checklist above, then decide whether a grammar-checking tool or a professional proofread is the right next step for your manuscript. Either way, the sooner you catch these patterns, the less they'll cost you when it matters most.
