Are you looking to go the "free" kind of route? This would be creating free accounts on web 2.0 sites like tumblr and then writing posts with links in them back to your site. For that, you could use GSA SER or SENuke. The more powerful (and not so free) method would be to drop catch expired domains which already have previous development or links coming into them. You would then develop those and link them back to your site. For that, you could use DesktopCatcher to find/catch the names. Then you would need to host them and develop yourself. Hope this helps!