1. Use past tense. USE PAST TENSE.
2. Don't use the "would" plus verb construction when the simple past tense would work. I.E.: "he would believe" as opposed to "he believed"
3. Avoid passive voice.
4. Keep sentences under control. A sentence is about a single thing.
5. Keep paragraphs under control. A paragraph is a collection of single things unified by a common idea.
6. Remember what your argument is.
7. Word processors can do lots of fiddly stuff for you. Let them.
8. Maps are Good Things.
9. Chronology is a powerful organizing device. Use it.