We've compile a list of all the things you can do to improve your car or truck's fuel efficiency:
 
1. Check your tire pressure at least once a month. Under-inflated tires burn more fuel. If tires are 8 pounds under inflated, rolling resistance of the tires increases by 5%.

2. At the pump, keep the hose in the tank until after the pump shuts off and make sure you allow all the fuel to pour out of the nozzle. As much as a quarter of a cup can pour from the hose. It's your gas, you paid for it, don't let it spill out onto the ground.

3. When appropriate, use your cruise control. This can save you up to 6% in fuel consumption on the highway.

4. Corroded battery cables cause the alternator to work harder, using more gas. Have them cleaned with each engine check-up.

5. Don't let the vehicle idle for more than a minute. Idling consumes half-a-gallon to one gallon of gas per hour and pumps needless CO2 into the atmosphere. The modern engine will consume less fuel turning off and re-starting than idling for extended periods. There are already no-idle zones in place in several counties. Also, to effectively warm an engine, drive it, don't rev it. Engines only work hard under load and will warm up much quicker if you simply start the engine, wait for 20 seconds as it builds the oil pressure, and drive away.

6. Change the air filter at least the set number of times outlined in the owners manual, more if you drive in dusty conditions.

7. Have a regular engine check-up. Since the advent of computer controlled fuel injection, there is no such thing as an old fashioned "tune-up" any more. At worst, you may be expected to replace spark plugs, oxygen sensor, or the air and fuel filters.

8. If your car was built since the mid-1980s, chances are it has an oxygen sensor in its exhaust system. It should be replaced just as you would spark plugs, following the 
manufacturer's recommendations. This little device trims the fuel delivery and has a profound effect on fuel economy in the process.

9. Driving in the highest gear possible without laboring the engine is a fuel-efficient way of driving. Driving at 35mph, a vehicle will use 25% more fuel in third gear than it would in fifth. Travelling at fast rates in low gears can consume up to 45 % more fuel than is needed. If you have an onboard trip computer, you probably have an "Instant fuel economy" setting.

10. Think ahead! Drive smoothly. By applying light throttle and avoiding heavy braking, you can reduce both fuel consumption and wear and tear. Research suggests driving techniques can influence fuel efficiency by as much as 30%.

11. Lighten your load. Think carefully about what you need on a journey. If you don't need something, don't pack it. Remove roof racks if not needed, as they create wind drag. The lighter the load, the lower the fuel consumption and emissions. An extra 100 pounds in the trunk reduces a typical car's fuel economy by 1 to 2%. Carrying excess weight wastes gas.

12. Choose the right octane gas for your car. Check the owner's manual to find out what octane your engine needs. Octane ratings measure gasoline's ability to resist engine knock. But the higher the octane, the higher the price. Only about 6% of cars sold need premium gas. Still, premium gas accounts for about 10% of all gas sold. Resist the urge to buy higher octane gas for "premium" performance.

13. Combining errands into one trip saves you time and money. Several short trips taken from a cold start can use twice as much fuel as a longer, multipurpose trip covering the same distance when the engine is warm. Trip planning ensures that travelling is done when the engine is warmed-up and efficient.

14. You can improve your gas mileage by 1 to 2 % by using the manufacturer's recommended grade of motor oil. For example, using 10W-30 motor oil in an engine designed to use 5W-30 can lower your gas mileage by 1 to 2 %. Thicker oil is harder to pump. This adds to parasitic horsepower losses.

15. Avoid "revving" the engine, especially just before you switch the engine off; this wastes fuel needlessly and washes oil down from inside the cylinder walls. This is really bad for the next start up, as the cylinder walls will be dry.

16. Drive steadily. Slowing down or speeding up wastes fuel. Also avoid tailgating. Not only is it unsafe, but if affects your economy if the other driver slows down unexpectedly.

17. 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 to overcome the drag.

18. Avoid rough roads whenever possible, because dirt or gravel can rob you of up to 30% of your gas mileage. Every time the wheels bounce up and down, forward motion energy is removed from the vehicle. Not only is it very uncomfortable, the vehicle will actually slow down from the transfer of energy. This causes the driver to apply more throttle, which wastes fuel.

19. Inspect suspension and chassis parts for misalignment. Bent wheels, axles, worn shocks, and broken springs can contribute to drivetrain drag, not to mention the unsafe condition they create.

20. SUV owners should consider switching from an aggressive patterned off-road tread to a fuel-efficient highway tread.