• Don't use no double negatives.
  • Eschew obfuscation.
  • Never use a preposition to end a sentence with.
  • The passive voice should never be employed.
  • You should not use a big word when a diminutive would suffice.
  • It is bad to carelessly split infinitives.
  • About those sentence fragments.
  • Avoid clichés like the plague.

(Just came across these on Advice to Writers, originally from William Safire.)