This is a pretty nice summary of best practices, though I would avoid using conditional comments altogether. Too bad it’s going to be at least half a decade before we can realistically begin to use HTML5. (via css-tricks.com)
Most of this isn’t HTML5 dependent - the doctype is prettier, and those <header> tags are nice, but not THAT much different.
Overall, a really nice overview.
Great overview
Source: css-tricks.com