1.  Go the speed limit and use the cruise control. Speed limits are calculated for maximum safety – they will also reward you with maximum gas mileage. You can get up to 20 percent more mileage traveling 55 mph than at 70 mph.  Using your cruise control also provides additional gas savings. You can save up to 14-percent savings, with an average savings of 7 percent by using the cruise control.

2.  Avoid lengthy idling and rush hour traffic.  You're burning fuel while idling (up to a gallon every hour). Avoid rush hour traffic when possible.

3.  Remove all the extra junk from the trunk.  The added weight in your vehicle reduces fuel economy, so take unnecessary items out of your trunk.

4.  Fill up when it's cool and before holidays.  By filling your tank during the cooler temperatures of early morning or late evening there is less vapor created. Filling up three days before a holiday will help you save on the per-gallon price at the pump.

5.  Don't top off gas and tighten the cap.  Stop adding gas when the pump shuts off automatically. Remember, your tank needs both fuel and fumes, so tighten the gas cap after every fill-up.  

6.  Use the correct fuel grade.  Use the fuel grade recommended by your vehicle manufacturer.

7.  Don't accelerate up hill rather build up speed before the hill, and then maintain it on the way up. Then you can coast on the way down for additional fuel economy.
 
8.  Avoid rooftop carriers.  Approximately one quarter of each gallon of gas is needed to overcome wind resistance, so avoid carrying things on your roof. If necessary, use an aerodynamic carrier to help minimize drag.

9.  Check your tire air pressures weekly. Buy an inexpensive air pump and an accurate tire gauge (not a pencil gauge as they are not accurate). Keep all tires inflated to the pressure as recommended for your car. Go by the tire wall; the sticker on the door frame, fuel filler flap, or manual is for comfort, not fuel efficiency. Generally speaking, a slightly higher pressure will improve fuel mileage and handling, but too high will degrade traction and wear the tires rapidly.

10.  Avoid having to stop. If approaching a red light, see if you can slow down enough to avoid having to actually stop (because you reach the light after it is green). Speeding up from 5 or 10 miles per hour will be easier on the gas than starting from full stop.

11.  Anticipate the stop signs and lights. Look far ahead; get to know your usual routes. You can let up on the gas earlier. Coasting to a stop will save the gasoline you would otherwise use maintaining your speed longer. If it just gets you to the end of a line of cars at a red light or a stop sign a few seconds later, it won't add any time to your trip. Ditto for coasting to lose speed before a highway off-ramp: if it means you catch up with that truck halfway around the curve instead of at the beginning, you haven't lost any time. (Do not coast to slow down until you're in the exit deceleration lane, unless you have checked your mirror to make sure you won't interfere with non-exiting traffic in the right-hand travel lane.)

12.  Take off slowly from a full stop. This is one adjustment that will have dramatic effects on your gas mileage; don't tear off from a stoplight or stop sign! If you move out slowly, it will help save you money at the pump. Also, if you are driving a stick shift, note that 50% throttle at 1200 rpm's uses less gas than 10% throttle at 2500 rpm's. As long as the engine is not lugging or pinging, shift as soon as possible and use plenty of throttle. The engine is more efficient when it does not have to pump air past a closed throttle plate. Warning: The last part of this advice is only true for fuel-injected cars or those with constant velocity carburetors.

13.  Park in the shade. Gasoline actually evaporates right out of your tank, and it does so faster when you park directly in the sun - winter or summer. Parking in the shade also keeps it cooler inside, and you will need less A/C to cool off when you get back in. If there is no shade available, park so that your gas tank (the actual tank under the car, not the valve to fill it) is facing away from the direct sun.

14.  Instead of running your AC, lower your windows; AC can waste up 15% of your gas, while having your windows and catching a nice breeze wont waste any of your gas. Plus you get fresh air into your car and yourself which is healthier for you. However, at faster speeds, studies have shown that the significant drag caused by sunroofs/windows being open nullifies the difference. The point at which AC is more efficient is at 35-40 mph.  

15.  Do not rest your left foot on the brake pedal while driving. The slightest pressure puts "mechanical drag" on components, wearing them down prematurely. This "dragging" also demands additional fuel usage.

16.  Make certain your gas cap fits properly.

17.  Use radial tires for less friction between tire and road.

18.  Keep wheels aligned for better mileage - Longer tire life, too.

19.  Tighten up that gas cap. Gas will evaporate from your car's gas tank if it has an escape. Loose, missing or damaged gas caps cause 147 million gallons of gas to evaporate each year, according to the Car Care Council. So be sure to tighten up that gas cap each time you fuel up your car.

20.  Use your garage for your car. Got a garage? Clear it out and make room for your car. Parking in your garage will help your car stay warm in winter and cool in summer, and you won't have to depend as much on your gas-guzzling air-conditioning or defroster when you drive.