A good place to start is http://html5boilerplate.com/. This provides a good starting point and includes the modernizr library by default, which makes it very easy to check for compatibility with HTML5 features like canvas, video/audio tags and websockets.
Dive into HTML5 by Mark Pilgrim has also been a helpful reference for me.
Dive into HTML5 by Mark Pilgrim has also been a helpful reference for me.