Depends on your niche but I find that by being where my customers are and getting my content in front of them as well as always being useful and helpful works well. I also network as much as possible and try and help out people in my niche that have a target audience I'd like to tap into.
I love Face Book and especially the fan pages which brings me tons of free traffic to my dating sites.
First optimize my seo. Second blogging. Article submission. Web directory submission. Social media. I do these steps as they are followed by each other. I at last use social media when everything is ready and optimized.
Google and social media has worked the best for me. I worked hard on optimizing my sites for Google, and I now get lots of traffic from it. I use Twitter, Facebook and Google+ to drive targeted traffic to my site. I also do forum marketing and article marketing which brings in some nice traffic too.