I found this on Gather; apparently it is one of those things passed around over email:
1. Verbs HAS to agree with their subjects.
2. Prepositions are not words to end sentences with.
3. And don't start a sentence with a conjunction.
4. It is wrong to ever split an infinitive.
5. Avoid clichés like the plague. (They're old hat.)
6. Also, always avoid annoying alliteration.
7. Be more or less specific.
8. Parenthetical remarks (however relevant) are (usually) unnecessary.
9. Also too, never, ever use repetitive redundancies.
10. No sentence fragments.
11. Contractions aren't necessary and shouldn't be used.
12. Foreign words and phrases are not apropos.
13. Do not be redundant; do not use more words than necessary; it's highly superfluous.
14. One should NEVER generalize.
15. Comparisons are as bad as clichés.
16. Don't use no double negatives.
17. Eschew ampersands & abbreviations, etc.
18. One-word sentences? Eliminate.
19. Analogies in writing are like feathers on a snake.
20. The passive voice is to be ignored.
21. Eliminate commas, that are, not necessary. Parenthetical words however should be enclosed in commas.
22. Never use a big word when a diminutive one would suffice.
23. Kill all exclamation points!!!
24. Use words correctly, irregardless of how others use them.
25. Understatement is always the absolute best way to put forth earth-shaking ideas.
26. Use the apostrophe in it's proper place and omit it when its not needed.
27. Eliminate quotations. As Ralph Waldo Emerson said, "I hate quotations. Tell me what you know."
28. If you've heard it once, you've heard it a thousand times: Resist hyperbole. Not one writer in a million can use it correctly.
29. Puns are for children, not groan readers.
30. Go around the barn at high noon to avoid colloquialisms.
31. Even if a mixed metaphor sings, it should be derailed.
32. Who needs rhetorical questions?
33. Exaggeration is a billion times worse than understatement. And finally...
34. Proofread carefully to see if you any words out.