People say guest blogging is a great way of creating backlinks but it is also the most difficult. You can send requests to 100 sites and maybe 1 or 2 replies back and let you create a guest post. While this might be a good way to rank, but you cannot put all your SEO eggs in this one basket. You need to do forum commenting, blog commenting, social bookmarking, article submissions to create backlinks on a regular basis.
That is what I have been doing for my website and blog about call center outsourcing and it has started to show results in terms of keyword ranking.