PageRank is only increased with backlinks - to get backlinks, exchange links with other blogs, ask other blogs and sites for links, and just get your site 'out there' - technorati, social networking, bookmarking sites etc.
Get more links. It's that simple. You're going to want quality relevant links of course; these are links on pages that are ranking well in the earch engines (top 1,000 results), have a PageRank of 4 or higher, are related to your niche, and contains the search temrs you want to rank well for.
Try to get more and more relevant Links and also from High PR page. Add more unique content on your blog.
Write high quality content regularly and people will naturally link to you. Comment on related blogs. Blogroll exchanges. Article submissions. Posting on DP and other popular forums with sig link. Etc.