I am doing many things like social bookmarks,forums post,article submission which is best to get backlinks
@OP: You'd probably get a lot more information here in DP by searching instead of posting threads which has been posted a gazillion of times! You can also refer to this blog post from http://googlewebmastercentral.blogspot.com/2010/06/quality-links-to-your-site.html which explains Quality links to your site and how you can possible get them by doing it the legitimate way.
To increase back link you have to practice all SEO tool but SMO is good one and effective.. Forums Directory Submissions Commenting Blogs
Stay away from directory submissions (there are a handful that are ok.... the rest are useless) and link exchanges. There are still plenty of ways to get backlinks to your site including articles, press releases and more importantly by writing good content on your website that other people will link too. Here's some more ideas for you. http://www.im-wizard.com/how-to-get-backlinks-to-your-website/
on their places are things are valuable so you have to all that things but first and most important thing is make quality backlinks
i think socialbookmarking and networking sites are best as you can just post the artciles/link without getting punished
You can use these too: Directory Submission, Social Bookmarking, pres relise, blog comment, forum posting
Regarding directory submissions, if applicable to your niche, make sure you are listed on local directories like Google Places, Yahoo and Bing. It's easy to forget to do this. Secondary to these would be Local.com, Insiderpages, Superpages and Citysearch. These seem to be the most recognized by Google.
Ask bloggers in you niche for a link, write press releases , write interesting articles that are informational and submit to article sites. These are the things that have worked for me in the past. It is not easy to do good SEO but very worthwhile in the long run.
For getting backlink use the following thechniques forum posting, areticle submission, directory submission, press release, squidoo, blog commenting, pay per click, link exchange...
I think article submission and directory submission are best for free backlinks. Social bookmarking are mostly nofollow.