Here are George Orwell's six rules for clear writing, from his famous essay on Politics and English Language:
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.
3. If it is possible to cut a word out, always cut it out.
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 say anything outright barbarous.