Has a somewhat similar writing style to yours. It’s fine to modify your style a bit to suit the blog you’re guest posting on, but if you’re normally very “out there” with lots of off-color jokes, and the blog you’re writing for is more conservative, you’ll either find that (a) they reject your post because your style isn’t a good fit or (b) you modify your style to suit them–and readers who click through to your blog come down with a fit of the vapors. Both situations result in a less than desirable outcome.

You’re proud to be associated with. Avoid guest blogging on sites that have been heavily criticized in your niche (unless you want to show your support for them), and avoid blogs that don’t fit with your personal moral or ethical values. If you’re a staunch liberal, for instance, it doesn’t make much sense to write a blog post that’s strongly in favor of a conservative ideology. The content won’t come off as authentic, and you’ll probably regret the decision in the future anyway.