The marketing guru Seth Godin compiled this list two years ago and it is still relevant today. Some of the stuff in the list includes, e.g. write posts that need to be read right now, learn enough to become the expert in your field, break news, write posts that will be readable in a year, be among the first with a great blog on your topic and encourage others to blog on the same topic, share your expertise generously so people recognize it and depend on you, announce news, write short, pithy posts, encourage your readers to help you manipulate the technorati top blog list,
don't write about your cat, your boyfriend or your kids, write long, definitive posts and much more. Enjoy