What should a professional blog have?

Should a blog have categories? (Videos, news, updates,). Should blogs have share icons? (Twitter,Facebook, Digg).
The question is, what do you think a blog must always have to become successful? Please post you’re opinion.

My blog is hosted by Tumblr. It has great content. (Going by a couple of reviews) But thats about it. Since I’m using a Pre-made Theme for my blog, it really doesn’t have much. But I am about to start coding my own for my blog. Right now I’m drawing sketches, writing ideas of what my blog should have. I really need some opinions on what features a blog should have.