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.
Hope this helps. Wishing you SEO success