Unfortunately, Owen TJ is correct. You're driving one of the most anti-aerodynamic vehicles on the road. Your fuel efficiency will never be more than marginal at best. Keep your engine tuned, run quality fuel, and drive responsibly. That's about all you can hope for, really. The trick of airing up your tires to the point they're hard as hell to save a buck or two in fuel only wears out your tires faster and makes the ride rougher.
Best advice? Get something more fuel efficient and use the Jeep as a 2nd vehicle. That's what I had to do when my Jeep got too big to drive everyday.