I have tried a bit of everything to grow my blog: participating in carnivals, signing up for contests, spamming Glenn Reynolds for attention (sorry Glenn). Here is the lesson I have learned: You have just got to write a lot. Other bloggers will notice you and start linking back to you when you write about them. Walter Olson at Overlawyered has had me guest blog a couple of times, and I don't think I ever emailed him once. I linked to a lot of his posts, adding my commentary, and he eventually noticed. Ditto some of the folks at Cafe Hayek, at Reason, and at the Knowledge Problem. In turn, I have discovered great blogs like Maggies Farm and Catallarchy from my traffic logs. Write a lot on your blog, and comment on other people's blogs, if you really have energy to burn, and the traffic will show up. Search engine traffic alone will bring new readers, and the more you post, the more different searches will find you (though some are a bit bizarre).
As a sort of reverse proof of this, here is my traffic profile for the last year. Nothing spectacular, I am just a small blog, but you can see what happened to traffic when my posting went way down over the summer. I have in turn been burning up the keyboard in September, and I hit a new traffic high.
Update: Trackbacks used to be a great way to tell folks that you were commenting on a particular post. Unfortunately, spam has pretty much killed them at most sites, including this one.