Write good and quality content, use h1 and h2 tags for headings, use relevant links, use keywords in title tags and description as well do press releases, article submissions, blog comments for your website.
To improve your PR you must make your content quality and unique, write articles and submit it different sites, same blog commenting also should be different sites, and for guest post you need to provide quality and unique content and finally every social bookmarking should be done in different sites.
The things you should do to get high PR is delete the unrelated and low quality backlinks in your website and concentrate on the content present in the website, then do off-page on article submission, web2.0, blog comments and forum posting will help to get high pr.
*Make sure that your site is optimized for the search engines
*Focus building your site on original and unique content
*Submit your site map to Google
*Submit to the main search engines, Yahoo, Google, MSN and any others
*Usage of NoFollow Links
*Submit to Article Directories
My site was in 2nd page for a two-phrase keyword. It was highly competitive keyword. In order to bring to 1st page, I did some promotion work like article submission, forum posting, blog commenting. All this I did with same anchor text. But my site went down. Now it is not in first 10 pages. Can any one tell why this have happened. And how to get back my site for that keyword.