When I first started my blog I never used to comment on anybody else's blogs. But readers of my blog always left comments on my posts. If they had their own blog their name above the comment would link to their blog. I would always click on the ones that had blogs. This would give traffic to their blog.
Nowadays I leave the regular 5-10 comments on other blogs, daily. Ever since then, the traffic coming to my site has increased. I wonder why... :D