1. Optimum Speed for Fuel Efficiency: The optimum speed varies per vehicle, the old standard is – Driving at 55 mph (90 km/h) is the optimum fuel efficient speed for the average vehicle. Driving at 75 mph (120 km/h) uses 20% more fuel. That’s 20% more $. New studies show that some vehicles may have an optimum speed for fuel efficiency higher than this old standard.
2. Reduced Breaking: Unless you drive a hybrid or vehicle that re-coops energy while braking, every second you brake the more fuel is wasted. You can reduce wasted fuel by not driving more quickly than is necessary. When possible, start slowing down before a stop is needed, the sooner you can take your foot off the gas, the less fuel wasted.
3. Keep the RPM low: there are two tactics here depending on your transmission type.
3a. Slower Acceleration: When accelerating quickly, you are accessing more power from the engine (the engine revs to a higher rpm) therefore using more fuel. Drivers who speed up quickly, and then hit the breaks at the last minute to stop are wasting fuel. Using cruise control can improve efficiency because it follows this method.
3b. Drive in a lower gear/speed: For manual transmissions, you can upshift to a higher gear (your rpm will decrease), meaning the engine is working less to maintain the speed. Yes this reduces power of the engine, but it increases fuel efficiency.
4. Plan your trips: Where you can organize the stops you have to make to reduce the distance you drive, and plan ahead to reduce the number of trips, this will impact your fuel efficiency.
5. Aggressive Driving: also is a fuel waster.
6. Warming up your vehicle: My owners manual for my vehicle says the car does not require an initial warm up, unless I will start driving on a highway or at high speeds right away.
7. Avoid Idling: If you do not know how long you will be waiting, turn-off the car while waiting.
8. Air Conditioning: uses fuel, heat does not. Reserve use of the A/C to necessary situations.
9. Avoid air drag on the vehicle: Driving with the windows down, roof racks, spoilers, etc. increase the air friction/drag on the vehicle. If choosing between driving with the windows down or using the A/C, the general rule is to use the A/C above 40 mph (72 km/h). Pick-up truck drivers, should you keep your tailgate down? There is evidence for both conditions, but for surprising reasons you should keep it up. Read this letter from the Car Talk brothers.
10. Travel Light: Do not load your vehicle with more than is needed for the trip, the more weight, the more fuel is used. Pick-up truck drivers can remove snow from the bed to improve fuel efficiency.
11. Regular Maintenance: Maintaining the tire pressure, change the air filter, and regular oil and filter changes all improve the fuel efficiency.
Similar and more detailed tips can be found on How to Save $ on Gas #1