But seriously. There is no way a blog should look; a lot of very slick and surprising things turn up now and then from rule breakers (see some ideas at css Zen Garden). There are quite a few good guidelines for how a blog should not look, though.
Among the major and most common mistakes is background and text that do not contrast. It’s difficult to read, if you couldn’t tell. If you don’t want your blog read, then by all means, go for it. Another pet peeve is forced justification and all caps. It doesn’t work. Being different just to be different is a mistake. If you don’t have a clear and rational reason for breaking traditional layout rules, don’t break them. The designers who came up with them were better at it than you are.
Rule of thumb—ask yourself, “Does the change make it easier or harder to read?” Blogs are for readers. Fancy design and colors impress no one, they just get in the way of dedicated visitors.