A website I stumbled across through del.icio.us today, Demon @ Thus, has a great short article on writing for the web. The article covers 10, easy-to-understand points, from which I shall paraphrase:

1. Keep in mind what you want to convey
2. Understand how people read and use the web
3. Be succinct and get to the point
4. Avoid linguistic complexity
5. Break up the text into digestable bits
6. Structure the information architecture content of each piece
7. Be aware of design
8. Provide detail
9. Place objectivity above showmanship
10. Write with a consistent style

Since writing for the web is one of the biggest parts of (white hat) SEO, it's probably a subject I will attempt to focus on more here at SEOmoz.