Look for details: using a longer lens are there interesting little features or details you can shoot. Some museums, particularly those about an individual, are often set out to look quite natural. Can you take a shot of an interesting environment? Use wider apertures to throw backgrounds out of focus.
You want to avoid using flash if you can. Firstly there is a good chance that flash photography will be prohibited anyway. Secondly, flash light often kills the very ambience that was appealing in the first place. Use the natural light of the building where you can.