help me for optimize google pagerank

hi guys

i have 4 domain for my forum
1 domain is main domain and other domains redirected (301) to main domain
all of my domains have 2 in google pagerank

what is the best way to increase main domain pagerank ?

Backlinks from other sites are the only things that effect page rank.

But, it's a useless metric. I wouldn't waste ANY time on trying to increase page rank. I've seen PR0's with 80x the traffic of PR6's.

Page rank mainly caluculated by dofollow backlinks via other webpages. and page rank isnot really something important. More important is to have real web traffic. If you want to increase page rank you should get alot of dofollow backlinks. Let's say an avarage 20 pr1 links can make you 2 at next pr update. Best way is social bookmark your site to dofollow bookmarking sites and submit the dofollow directories such as dmoz.org on the web. But it'll take time. Latest page rank update happened after 9 months of period. So you need to be abit patient to see next update results.