How to get strong back links to my site?

Google your niche for forums and join the top five. Make sure there is a link in your profile, preferably in the signature and post often but don't spam. Google for indirectly related niches (read as non competition websites) and contact the webmasters of the top five to see if they would like to reciprocate links. Write a blog! Write a how to for any how to site and include your link. Answer questions on yahoo answers (see my sources for an example.) Get creative and search for ways to have your link on someones site. Or you can pay a back linking service.