What you can do
- Review the specifications and send comments! (See below for details.)
- Help to write the FAQ.
- Write articles about HTML5 on the blog.
- Write tutorials for new authors and for authors moving to HTML5.
- Monitor and respond to questions on the help list and the forums.
- Write test cases.
- Write demos (ideally in a Google Code project).
- Implement HTML5!
- Edit one of the many companion specifications that are lacking editors.
The most useful thing from an authoring standpoint would be going through the spec and finding bits that don't make sense. Start with the authoring view:
element, and you couldn't work it out. Then you would file a bug "I couldn't find the answer to the question 'What elements are allowed inside <p> elements'.".