Fix your Title and Meta tags. Remove the hidden comment tags with stuffed keywords. get some links pointing to your site.
Do off page like directory submission, Article sub, Blog posting, Social bookmarking and check your on page meta tag is descriptive way.
Get links from authority blogs and websites beyond that your page needs to be on page optimzed in url,title,paragraph's first word,bold keywords in paragraphs ,tag optimized. Another way is get back-links from variety of domains and not all links from same domain.Get links from domains that have less than 30 outgoing links.Apply Link wheel technique from dominant pr's..
to be honest the best way to improve your PR is to not ask such a question on a forum where you will get 20 different answers often excluding each other (how do you know which one is right?). In addition that answer depends on what your site is worth now. The best way to improve PR is to get good training, from good source like Aaron Wall.
I have been trying to build up my backlinks . I am currently at PR2 for a long time and want to push up my site to PR4 by end this year. I would really appreciate if anyone can teach me a sure proof way of doing it.
You need one way, do follow text links from relevant pages with strong PR and low outbound links. If you look carefully, you can find good resources that offer exactly that.
Build useful backlinks. That means relevant links for your blog/site. Then update the blog regularly. You can easily get good page rank.
Build useful back links.But make sure you write an attractive description for your description meta tag. This gets listed first to the visitors when search engine find your website relevant for that keyword.