CNNMoney has a great article about how to make the money you spend on gas go as far as it can. (I've edited it down for space.)
Here's a few ways you can WASTE gas that you might not know about:
1. Racing away from green lightsWhen the light turns green, you don't have to take off as quickly as possible. That pedal under your right foot is called the "gas pedal" for a good reason. The more you press down on it, the more gas you're pumping into the engine.
2. Racing up to red lightsWhen you're driving down the street, and you see a light red light or stop sign up ahead, you should lay off the gas sooner rather than later.
Let off the pedal sooner and give your engine a rest as you coast to the stop while braking gently. As an added benefit, your brake pads will last longer, too.
3. Confusing the highway with a speedway
Even if it doesn't involve hard acceleration, speeding wastes gas. The faster you go, the more air your vehicle has to push out of the way. In tests by Consumer Reports, driving at 75 miles per hour instead of 65 miles per hour reduced fuel economy by between 3 and 5 miles per gallon, depending on the vehicle.
4. Bumper-buzzingEvery time the driver ahead taps his brakes, you have to slow down even more than he did. Then you accelerate again to get back up to speed and resume your bumper-buzzing routine.
Hang back and you'll be safer - plus you'll be able to drive more smoothly and use less fuel.
5. Driving standing stillIdling burns about a half-mile worth of gas every minute, according to the California Energy Commission. Now you don't want to shut your engine down for every little stop in your regular, non-hybrid car - it's not designed for that - but if you're waiting for someone to run in and out of a convenience store, turn off the engine. And don't go through the drive-through at fast food restaurants. You're already paying enough for the oil in those chicken nuggets.
6. Short hopsFor really short trips, take advantage of the opportunity to get some exercise. If you can't hoof it, save up your errands. Go to your farthest destination first so your engine has a chance to reach its optimal operating temperature. Then make your other stops on the way back. With the engine warmed up, the car will restart easily and run efficiently all the way home.