Use Jp Magazine's patented gas pedal hoop.
Pros: You can be the envy of all your friends and save gas at the same time. You can even color-code it to your Jeep.
Cons: Get a mad trucker or ricer behind you, and there is no way for you to accelerate out of their way. Sometimes half throttle sucks.
Adjust your carburetor properly. Use an O2 sensor/gauge setup if needed to figure out if it's running lean or rich.
Pros: It's a good excuse to get that wide-band O2 gauge you've been looking at. It will save you gas, after all.
Cons: You'll either end up in a wreck from not watching the road or you'll start obsessing over your air/fuel ratio.
Driving Style Changes
The biggest changes are to be found by simply changing your driving style. For one, it's free. Two, it's ... um, well, free. FREE GAS!!!!!
Leave a greater following distance.
Pros: By leaving a greater following distance, you will hit the brakes less. Additionally, you will not hit the gas as hard to maintain that five-foot following distance at 80 mph after hitting the brakes.
Cons: You'd better not be in a hurry to get anywhere, 'cause even grandma will be cutting you off.
Avoid quick, jackrabbit-like starts.
Pros: You'll let your drivetrain live longer if you don't think you are in the NHRA.
Cons: You might as well drive a scooter. Jumping the gun at lights, especially with deeper gears, is a lot of fun.
Put your top up.
Pros: There are huge gains to be found from running with your top up. Two to three mpg is not out of the question.
Cons: With the top up, most of the fun of Jeep ownership is gone. Might as well get a Liberty.
Keep your speed down. By going 65 mph rather than 80 mph, you can see as much as a 45-mile increase (usually closer to 25 miles) in a tank of gas.
Pros: Better gas mileage (duh). In short trips, the time lost from going slower isn't a big deal
Cons: There is no way you'll get where you want to go beyond 20 miles away within any reasonable timeframe.
Random Junk
By "junk," we mean it.
The best way to save gas with your Jeep is to get an econobox.
Pros: 30 mpg is suddenly reasonable. Find a cheap enough junker, and that $2,500 buy-in makes sense if you have a long commute.
Cons: If any of us wanted to drive one of these, we'd work at Import Tuner, or be reading it. Plus, it'd take a 10-inch lift to clear 31s.