Internal linking raises your PR.
Even more important than having the proper keyword density is linking your pages correctly internally. It's probably the most overlooked aspect of good SEO.
You can have every page inside your site link back to a single page and raise it's PR just from the links you created. It's better than nothing, right? A large part of SEO at this point is naming your anchor links and using them internally. You will notice through out this site we link to certain pages within our text. This is both to help you navigate through our internal SEO strategies, but to also help the search engines by showing them what pages are important to us.
Think about this SEO strategy from a e-commerce aspect. Would you rather have a high Terms Of Service page or a high Ranking Sales page? I know which one I would prefer.
A basic crash course into this internal linking strategy is to make sure that every page on your site passes PR back to your home page. This can be done by simply adding a anchor text link to the footer of your website (look we did it here).
You can also link every page on your site from your site map
if you have "orphan" pages that need to be spidered by the engines that you
don't include in your menu. A sitemap is a basic page that has a hyperlink
for every single page that you want the search engines to find.