Which engine and what kind of transmission? Is it a 4x4? How much city driving vs. highway driving? Have you had a tune up lately?
If that’s city driving, it’s probably not going to get much better. If it’s mostly highway (and you have any motor other than the 460), you should probably be getting a little better, though it may just be a matter of slowing down.
Assuming the engine is in good tune, the bearings are turning good, the brakes aren’t hanging up, etc there’s probably not much that’ll help the mileage. If you’ve got a V8 with a 2bbl carb, putting on a sequential 4bbl might help a little (assuming you can keep your foot out of the secondaries).