1. Ask yourself: What do I want to say?
2. Say it.
3. Say it shorter.
People think if they state their ideas plainly, others will think these are obvious, simple ideas. So they try to cover it up, using big words and long sentences.
Substance comes before style, so first you make your point. Then you chop it down.
(Personally, once I'm done writing, I set out to cut it by 20%)
Kevin Kelly wrote this same advice differently, he said you can't write and edit at the same time.