How do I clean up a bear skull?

The easiest way is to call a taxidermist. If you're looking for an organic method, there's a critter called dermistic beetles that will clean them up. If you rely on ants, beetles, or other insects be sure it is in a wire cage of some kind to foil the bigger animals. Cooking may be the most common method. Remove what you can first. Hold the water temperature below a boil so you don't yellow the bone or loosen the teeth. Cook and scrape. Cook and scrape.