The whole idea of link building has been debated to death and there are numerous theories and 'black hat' tricks out there. Here are some tips that will help you increase your Google page rank effectively.
1)The higher the page rank of the site that links to you the better, but relevance is equally important. Make sure that the site that links back to you is at least in the same niche as yours. Random links mean nothing to Google - remember that it is all about perceived importance and relevance.
2)Build your links gradually. Google's robot is not as stupid as many people make it out to be. If you get 100 links in one day this will definitely red flag your site. The best way to do it is to gradually and consistently build links back to your site.
3)One way links rule! A one way link is worth much more than a reciprocal link. Many so-called 'link farms' act as link exchanges where you can exchange links with other sites in your niche. Although Google value one way links more than a reciprocal links, it still counts - we just don't know how long for. As far as I can gather Google does not like link exchanges.