Google Blogoscoped presents these ten rules of Good Blog Writing Style:

1. Use descriptive headlines.
2. Write in "inverted-pyramid" style (get to the point at the beginning, elaborate in later paragraphs)
4. The first link is the one people click on, so make it the main link of your article.
5. Reintroduce core ideas in longer posts.
6. Use lists, images, tables and anything else that will make your artiles easier to scan.
7. Use simple language if you're writing for a global audience.
8. Credit your sources.
9. Mark updates and changes.
10. Spellcheck your posts and re-read them for clarity.
11. Note that all these rules have exceptions; know when they apply!