If you want to increase your Page Rank, you should build an essential quantity of quality backlinks leading from other websites to your site. It is advisable that such linking websites have also at least decent Page Rank (3 or more), because Page Rank is passed through the links and the higher PR of external linking resource is, the more it will contribute to your website.
Usually, when specialists talk about PR increasement they highlight the importance of building overall quality website (useful content, optimal user experience) rather than just sculpting impressive PR. http://moz.com/blog/how-to-rank, http://moz.com/ugc/google-pagerank-still-relevant-after-all-these-years, http://moz.com/article/search-ranking-factors
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