If you want to increase the pagerank means build more backlinks to your site.Backlinks helps you to increase the pagerank.The more backlinks means more pagerank.
you can also do blog commenting(dofollow blogs) and you can even get good back links by submitting your site to directories manually, actually there are many ways to acquire good back links all you need is hard work and patience in order for your website to have a page rank and to rank on top to different search engines.
PageRank is becoming just another factor in Google results, an a less important one it seems. Last year I saw our low PR sites shoot above other, much higher PR sites, as well as huge reshuffles in the SERPs, and from what à could see, whilst PR was a factor, it wasn't the deciding factor in where the sites were positioned. Worry less about your PR, and more on building a solid base of backlinks, with good, relevent anchor text, and get your on page SEO done well too.
Getting more backlinks helps you gain more pagerank.You can get more backlinks by commenting in blogs,article submission,social bookmarking ,forum postings,directories submissions etc.These help you to drive more backlinks.
Improving your site's PR is a continues hardwork, using a submitter is not advisable and it could make a negative effect to your website. Backlinks can easily gain from forum posting, social bookmarking, social networking, directory submission, blogging, article submission and so much more...
For improving Page Rank you have to collect good quality of back link for your website and the back links are come from high PR blogs and sites.