That possibly as broad a question as you could ask
Have you looked at
http://www.about.com
http://www.webmonkey.com
http://www.devshed.com
http://www.webreference.com
http://www.internet.com
Ideally you'll be wanting to look for the html sections of those sites and the tutorials mentioned.
At the end of the day though there isn't really a magic bullet for this one. Just like learning any language it takes time. He could just WYSIWYG it I suppose, but it doesn't sound like that's what you're looking for.
Just a thought. Is it design theory he's looking for, or practical texts?
Greg Moore