Link building process is a continuous process which includes - directory submission - article submission - press release submission - link baiting - 2 way or 3 way link exchange - social bookmarking and social networking etc... it is very important to get back links from only relevant theme of sites.
Get links to your site. The link in your signature, for example, is a link that points to your site. You could 1.) Buy links 2.) Get them manually with some viral marketing and good content posts. 3.) Comments on do follow blogs. Just a short list out there, but the fact remains that you need to get links to your site. Do it consistently, and try and acquire them from niches relevant to yours.
Always try to make BL from relevant site. You can go for article submission, blogging, directory submission. The most important is participate in different forums which allows dofollow signature. This the easiest way to promote the site and get quality BL