Create share buttons (Facebook, Twitter, Stumbleupon, Linkedin, Google+, etc.) for your content.
Build share function to Facebook, Twitter, Linkedin, Digg, Reddit, Blogspot, Stumbleupon, etc buttons on all content in your website. Make sure your blog has that function so users can easily share your blog to their friends.
Extra Tip: If your website has some kind of score or recognition (badges), you should also have share buttons to allow them to brag about it to their friends. Their friends would them come to try to get the same achievements as well. Because hey, people like to do what their friends do.