1. Avoid Alliteration.
  2. Prepositions dangle awkwardly if you use them to end sentences with.
  3. Avoid clichés and colloquialism like the plaque, or you will seem old hat.
  4. Employ the vernacular, while eschewing arcane and obfuscate verbiage.
  5. Avoid ampersands & abbreviations, etc.
  6. Take it easy with parenthetical remarks (however relevant) to avoid chopping up sentences (unnecessarily (we might add)).
  7. To ever, however artfully, split an infinitive, marks you as grammatically challenged.
  8. Skip the foreign words and phrases you know, n’est-ce pas?
  9. Never generalize.
  10. ‘I hate quotations. Tell me what you know’ Ralph Waldo Emerson.
  11. Comparisons can clog up writing as badly as alliterations and cliches.
  12. Avoid redundancy and verbosity, or readers will think you are repeating yourself and using too many words as well besides.
  13. We really get @*&%$**)!! when you use vulgarities.
  14. Clear, specific writings beats vagueness, we suppose, Whatever.
  15. Overstatement totally destroys any credibility you ever had before.
  16. Understatements can, at times, perhaps shade a point to the point of it’s fading a way.
  17. One word sentences? Eliminate.
  18. Analogies work about as well as fur on a flounder.
  19. “Is” just sits there. Pick verbs that mean something.
  20. Even if a mixed  metaphor sings, you should derail it.
  21. Who needs rhetorical questions?
  22. Its dstrakting too punctuat, an spel rong?

Update: I received that list from a friend, years ago. I have no idea from where it comes. If you know the author, please tell me and I will give credit.