From my experience, the most important things for HTML are:
use CSS, never hardcode styles
a correct template system: include dynamic content in a static layout, rather than include static content (e.g. header) in dynamic pages. Both TT and Mason supports this.
Comment on Re: Quality Standards Proposal to HTML Developers?
Our single most important thing is CSS and templating.
Er, our *two* most important things are CSS, templating, and strict guidelines on page-load speed.
Wait, I'll come in again. *Amongst* our most important things are....