I was just reading this article recently, which has some great tips and ideas. It's pretty thorough and goes into great detail:
12 Scalable Link-Building Tactics - Moz
The method in particular that I found interesting, was finding outdated content on other sites, and updating it for them in exchange to backlinks back to your site.
12 Scalable Link-Building Tactics - Moz
The method in particular that I found interesting, was finding outdated content on other sites, and updating it for them in exchange to backlinks back to your site.