What you can do
- Review the specifications and send comments! (See below for details.)
- 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.
- Help to edit the FAQ.
- 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:
Then use the widget at the bottom right (it says "Click the location of the error to select it, then type your message here:") to submit review comments on the spec. The best review comments are those along the lines of questions you couldn't find the answer to. For example, say you wanted to find out what elements you could put in a <p> 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'.".