Your Manuscript Deserves to Get Rejected If...

1. You send your sci-fi masterpiece to a romance publisher.  (Seriously, EVERY advice blog out there says "choose an appropriate publisher" -- which means that many, many people must not be doing this.)
2. You don't know the difference between "affect" and "effect," "principal" and "principle," "guild" and "gild."  (There's such a thing as being competent in written English, people.)
3. You have to go to a bookstore to find publishers in your genre.  (Seriously.  If you don't have a bunch of books in your genre, if you haven't already read a bunch of books in your genre, you have no business writing in a particular genre.  I've read literally hundreds of fantasy novels in the past couple of years.)
4. You don't know when to use "who" versus "whom" or "fewer" versus "less" or "between" versus "among."
5. You think it's really cool for all your characters to have apostrophes in their names, or umlauts, or cedillas, or other diacritical marks.  Or "y" instead of "i" and "e."
6. Your manuscript includes a farm boy (or kitchen boy) who turns out to be the long-lost son of the king, and who will one day be king himself.  (It's been done before, people.)
7. You think "older than him" or "taller than her" are grammatically correct constructions.
8. You're writing fan fiction of any stripe.
9. You don't include your SASE (or postcard, depending on what the publisher wants).
10. You send unsolicited manuscripts to publishers who don't accept unsolicited manuscripts.
11. You don't follow the instructions for submission on the publishers' websites.
12. Your magician characters shoot fire or lightning out of their fingertips, Emperor Palpatine-style.
13. The whole plot of your novel turns on (a) prophecy, (b) dreams, (c) a war between/among some gods you made up.
14. In your novel, characters speak in dialect which you spell out on the page (this was hard to read even in Huckleberry Finn, and you are NOT Mark Twain).
15. You feel the need to make up words in your own special language for everyday, normal concepts like "breakfast."
16. You just know you've got the next great book about a guild of thieves or assassins.  (This concept is tired NOW.  Trust me.)
17. You're a 15-year-old homeschooled kid whose parents think you're the best thing since sliced bread.
18. You're writing a book set in America, with American characters, but use British terms like "pram."  (Seriously, no one in the US says this except perhaps British expats.)
19. You just know you've got the next great book about vampires and/or werewolves (again, it's been done).
20. You think it's OK to use the same word three times in two lines (assuming that word is anything other than a simple article or conjunction).
21. You have named your characters systematically after rocks/gems/minerals, flowers, colors, or species of toenail fungus (OK, I don't know how many of that last one there actually are, but you get the point).
22. You have named some of your characters after your friends and others with fanciful, unpronounceable names you pulled out of your ass.
23. You include a group of primitive natives who have regular contact with a developed society, but who don't change their ways in the smallest part.
24. A horse in your world only costs as much as two beers at a tavern.
25. You're writing third-person limited and your characters describe their own appearances, to themselves.
26. You have two or three or more moons, and you have ships, and you don't consider how the multiple moons would affect the tides.   Or the calendar, for that matter.
27. You infodump because you're so proud of the history you've created for the towns in your world.
28. You think fully-trained mutant attack dogs can be created in 8-10 days from a bit of DNA and nothing else.
29. You think 3000 years is enough time for the human race to split and evolve into four or five separate species.
30. You think you're being original when your secret order of mages has cloaks that are "darker than black" (unless this is intended to be a tribute to Gene Wolfe).
31. You take normal English words and use them inappropriately ("scree" does not mean the same as "scry," and "consort" is not a verb that means "to marry").
32. You've written a bunch of (probably awful) poetry and include it in your novel (even if accompanied by a minstrel or bard who declaims or sings it).
33. You have a character who withholds information solely because it would ruin the story to have it earlier.  ("You're not ready for that knowledge yet, grasshopper.")
34. You include "teaching" scenes which are not-so-cleverly disguised infodumps.
35. You think that a standard crossbow is capable of firing several times a minute.
36. Your world once had dragon overlords who died out under mysterious circumstances, possibly only now making a triumphant return.
37. You've made some extremely common substance (e.g. a base metal alloy) more precious than gold.
38. Your villain exists only to kill, torture, and maim.
39. Your hero is a Mary Sue (or the male equivalent).
40. You use your thesaurus and pull out words like "bedight" or "sennight" which are specifically listed as archaic, when there are other, commonly-used words which will do just as well.  (Your readers don't want to have to use a dictionary to get through your fantasy novel.)
41. You have an army of millions.

Look, I could go on and on, but you get the idea.  Feel free to add others in the comments, by the way.