I think a lot of it depends on what you are selling and where you are selling it. That being said, and not having a ton of information to go off of, I’ve had good success marketing on Facebook. Definitely focus on your blog and building up your SEO though.
datpiratelife4me is correct. Also, I would try Instagram if you have great images. I’m not sure what you sell or offer. I’ve received some good traffic from twitter also. I usually try the free or low-cost options first then go with paid options or ads.