Though it is very common, let us talk about posting comments on blogs. The easiest way, yet effective form of Link building is through blog posting. Making at least 10 sensible comments to blogs related to yours would certainly make a difference. You need to be true to your comments, in that way you would build a good relation to the writer. SEO isn't just about traffic, traffic and traffic. As a blogger, of course I want my reader to learn from my writings and keep them from coming back.
Spending at least an hour to make a comment could help add visitors to your site.