Ok well there is no "set" think when it comes to blogging. Maybe like @theboredgamer says blog about your opinions and thoughts. Also blog about thinks you like and are interested in/good out i.e:
Hope this helped :)
answered Jan 24 '13 at 13:01
Blog about something you like? or something you're interested in. More specifically, your opinions and views on that topic. Or what a lot of people do is just keep like a public diary type thing, and post things about how you're feeling and life events, and things you like/dislike.
Really, a blog can be anything you want it to be. Good luck! :)