Social bookmarking, SEO, article submission, social networking (Facebook, Twitter, depending on your target group and product/service), quality posts, your Youtube channel. I've never bought traffic, but if some company provides such service, gives you targeted traffic, this might help a lot, though you might need to think, if buying traffic is good for your blog or not. I guess this is only good when you're providing some services or selling some product. Otherwise, it may be just a waste of money.