without a doubt its communicate with your readers and fellow bloggers. Nobody wants to read something when they get nothing back. Not only that but you make great contacts and open up your blog to guest posts and much more.
Appreciate your commenters - if they ask a question, answer it. If they take the time to offer advice, send an e-mail back and thank them. I normally e-mail all of my commenters and you find that they come back :)
Read other blogs. This is #1. Comment, interact, and get to know one another. These are your peers and your biggest fans. Twenty Something Bloggers is an amazing place for support, help, laughs and lifelong friends. You get what you put in.
Be yourself - don't try to do what someone else is doing because it seems to work. Your own voice is the only one you should try to put out there. It'll work better than anything else you try to mimic.
Add a question, poll, survey, etc to a blog post to make it interactive for the reader. It gets people involved and it's good to get to know your readers perspective on your post topic.