1. Never use a metaphor, simile, or other figure of speech which you are used to seeing in print.
2. Never use a long word where a short one will do. (Hemingway was the master)
3. If it is possible to cut a word out, always cut it out. (My personal favorite)
4. Never use the passive where you can use the active.
5. Never use a foreign phrase, a scientific word, or a jargon word if you can think of an everyday English equivalent.
6. Break any of these rules sooner than saying anything outright barbarous.