One mistake that a lot of newbie webmasters make is that they forget that Google ranks individual pages, not sites in general. So they tend to only build links to the main top level domain of their sites and not to the individual pages.
Of course you should probably focus on that main page, since it will sum up your site's content and visitors can reach each page from it with one click. But it should be remembered that each page is another opportunity to snare some nice targeted search engine traffic all on its own. So make an effort to target some good keywords for each (but not too many) and then build backlinks with those in the anchor text (while remembering to vary it quite a bit).
I've been using this technique with my SEO site and I've seen a real difference in the amount of search engine traffic I'm getting to those pages with a few backlinks. Needless to say, they get many more direct visitors than those with no backlinks at all.