Are You Setting Up WordPress For SEO Success? (SEOMoz article - great explanation)
If you want to know anything about SEO, SEOmoz (where this article was found) is one of the first places you'll need to start. Everything you need to know about properly optimizing your site (at least the on-page factors) for SEO is here. This is also explains the two plugins you'll need (Wordpress SEO plugin and Google Analytics - both by Yoast). Read it!