Good follow-up posts on this one. A few things to consider when working on improving your page rank:
1) Don't spam the search engines. I believe the term you may want to search for is "keyword to content ratio".
2) Build one-way links when possible on similar sites. Recipricol links are ok, but search engines really like 1 way links (i.e. from other sites to yours).
3) Keep content fresh. Update your site frequently. Add new content for your users.
4) Amazingly, this seems to work: Pay for google AdWords. I've seen many sites bump 1 or 2 points in PR just by having AdWords set up. I'm not 100% sure if this is "accepted" methodolgy, but for some reason many of the search engines follow those links and treat them as one-way. Also those ads end up on content relevant sites as well.
Hope this helps.