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. 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. Don't use no double negatives.
12. Proofread carefully to see if you any words out or mispeld something.
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 cliches.
16. The passive voice is to be ignored.
17. Eliminate commas, that are, not necessary.
18. Use words correctly, irregardless of how others use them.
19. Puns are for children, not groan readers.
20. Eschew obfuscation.
--compiled from various similar uncredited lists online