What you can do
So you want to take part? You can!
- 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.
- Maintain the document explaining the rationale of the decisions behind the spec. (See below for details.)
- 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'.".
See also Reviewing HTML5.
A rationale document
It basically would consist of watching the e-mail lists, the bugzilla bugs, IRC, and chatting with Hixie, and then writing documentation to explain the thinking behind different parts of the spec on the rationale page.
It could be as little work or as much work as you would want it to be. One could easily imagine this becoming a group effort.