I’d agree with Doug’s suggestions except as regards the length of posts. I don’t think they need all be short, “newsy” entries. I happen to like the essay format, and a well-formulated, researched case made on a particular subject is a useful resource to those of us routinely having to defend the secular, rationalist, and scientific points of view.
I don’t think it should be either/or, and sometimes there’s room for a longer essay in a blog entry. But if you look at the most popular blogs, they are pretty much universally short-form entries. My concern is that many bloggers think of the medium as being like writing a newspaper or magazine column. While a blog can look journalistic at times, it’s a different literary form than a magazine column—shorter, more easily digestible, with links to more detailed information for those who want to drill down.
It should also have a clear point of view; it should be opinionated and personal. That’s why I don’t think that corporate blogs work.