Do not be confused by the PageRank of a webpage which is Google's view of the non-keyword specific authority of the page and the page rank of a webpage which is its ranking or positioning on a search engine results page.
PageRank is on a logarithmic scale with new websites having PR0 and the top authority pages, such as Google.com having PR10. PageRank of webpages depends on the number and quality of incoming links.
The best way to increase PageRank is to produce high quality content that other websites will wish to point to - link-bait. It is acceptable to produce articles and write comments on forums and blogs with backlinks to your webpage provided these contribute value to the internet.
Google frowns upon artificial mass produced links particularly if you use programs that disseminate spun versions to acquire thousands of links. Recent updates to the Google algorithm - Panda, is Google's antidote to this and if you take that route, Google may punish you for it.
To increase Pr of your site you have to promote them by various off page techniques as Forum posting, Article submission and Blog creation and updation. You can submit your site to various free or paid directories. By using these techniques, you can increase back link of your site, which also helps in PR.
Page rank is an elusive term that most bloggers don't completely understand. In fact, there are probably few people in the world who completely understand it. Secrets of its page rank algorithm very guarded. Boosting your page rank isn't something you can do in a day. If it were, everyone would have a Page Rank of 10. Keep reading to learn a few of the tricks to increase your blog's page rank that are fairly easy to implement over time.
Some good points to get a page rank :
1 Get Incoming Links from High Quality Related Sites.
2 Remember to Use SEO Techniques.
3 Write Original Content.
4 Don't Go Link Crazy.
5 Write Great Content.
David above has said it best. Many people obsess our PageRank when they should really focus on SERP (Search Engine Rank positioning or Search Engine Results Page) is much more important. You can get PR by getting links from a few high-PR pages but it does not guarantee that you will rank higher in search results for your chosen keywords.
According to my knowledge it takes some time, you have keep patience. You have to use fresh and quality content which is most important for improving site rank. Use White hat SEO techniques which is good for your site.
Backlinks are necessary for improving site's PR and Off page SEO techniques are used for generating backlinks.
I mainly prefer Forum posting, Blog posting and Social bookmarking for getting backlinks.