Take a look at this thread: http://forums.digitalpoint.com/showthread.php?t=204881 It should answer most of your questions. PR is based upon many things.
Get more links to point to your site to improve your pagerank. The amount of PR leaked to your site depends on the current page rank of the site linking to you, as well as the number of outgoing links on it........
Backlinks are most important.So,try to get more and more QUALITY high PR backlinks to increase the PR.High PR backlinks will get you good PR. Also , quality backlinks are important for SERPs aswell .
you should try getting as many related links you can. as an google article said, Google does not really check how many links you have, they check where links are from. This is something like: Quality is king, not quantity.
for increasing your backlinks, you need backlinks from high pr and low outgoing web sites so two of the thinks that you mention is important