1) Re-design: A good looking (user friendly) site gets instant PR updates. 2) Content: Change all your content in a way that has less keyword density but is exclusive in its material. You'll see quick PR improvements. 3) Backlinks: Buy some good blog comment backlinks frequently from PR1-5 pages. (<50 OBL). They'll boost up while working on background level. In past, I increased PR from PR0 to PR5 using above.
you need to build more relevant and high quality back link to get good PR. Also concentrate on original content while promotion, it may affect your ranking.
the best way to increase your PR is by adding your link on other High PR website, and the best one of all links are homepage URL, which you can easily get if you visit the site mentioned in my signture.