Blog blogging, a discussion.
This doesn't necessarily mean that you will have to be a recognized expert on the subject, although it would help to have more than a casual interest in what your blog is all about. Keep in mind that your readers will gradually come to depend on your blog as a source of information that they cannot get anywhere else, and being knowledgeable in your niche would ensure your reputation as a person of authority. Under no circumstances should you steal content from other websites. Even if you have nothing to post on your blog for a few days, this is still a lot better than stealing content from someone else. Keep the golden rule in mind, and don't rip off content if you don't want other people ripping off content from you! Finally, always write as if your reputation is at stake.