WebTeam

One of the points of CSS is to separate style from content so that search engines have better clues as to how your pages are structured — that way, they can better tell what your pages are about. This is one way of describing “semantic markup,” which is making sure your structural markup tags (title, p, h1-h7, especially) reflect what you want search engines to think your page is about.

Pearsonified has a good basic guide which is aimed at WordPress bloggers, but which would help anybody.