If your site is not achieving the page rank you think it deserves: check the following.
Server is Often Inaccessible to Bots -
Content is similar to or Duplicate of Existing Content in the Index
External Links to Low Quality/Spam Sites
Duplicate Title/Meta Tags on Many Pages
Participation in Link Schemes or Selling Links on Your Pages

If any of these apply to your website or blog, your page rank will suffer.