This slideshow is a must watch for anyone blogging. I think it makes some good points. I totally agree with three points:
No one wants to read a broken record. (vary your content)
No one wants to write a broken record .(vary your content)
Sometimes your blog posts should be easy to write.
I do want to add that commenting is a very important part of blogging as well. If you join in the conversation and be a part, people are more likely to come see what you have to say. (Goodness knows, there are enough know it alls in the world!)