Make your commentary form friendly and inviting. With so many available forums, I’m likely to choose those that cater to my communication preferences. For example, some blogs force me to use my Google ID. Since I don’t access my Gmail account, I’ll never see follow-up comments; why bother composing a thoughtful comment? 

I know there are ways around that, but why should I have to do extra work to contribute to your blog? I find that many folks don’t like to leave public comments, but they love more personal contact. If you don’t want to provide an email address, consider creating a simple contact form.