Do not stay in high gear if the engine labours
Be mindful that short journeys use more fuel
Make sure the engine, gearbox and rear axle oil levels are correct for your vehicle
Schedule routes to ensure minimum mileage
Avoid High Speeds: As your speed increases, your aerodynamic drag increases drastically. Driving 55 mph (88 km/h) vs. 69 mph (110 km/h) on a Highway will reduce fuel consumption by up to 20%.
Automatic Transmissions should be allowed to cool down when your car is idling at standstill for example at Traffic Lights. By putting the gear into neutral position, this reduces transmission strain and allows the transmission to cool.
Do not accelerate or brake hard. By anticipating the traffic and applying slow steady acceleration and braking, fuel economy may increase by as much as 20%.
Keep tyres properly inflated: Keep tyre air pressure at the level recommended by your vehicle manufacturer. A single tyre under inflated by 2 PSI, increases fuel consumption by 1%.
Use A/C Sparingly: When the air conditioner is on it puts extra load on the engine forcing more fuel to be used (by about 20%). The defrost position on most vehicles also uses the air conditioner
Do not keep windows all the way down: Open windows, especially at highway speeds, increase drag and result in increased fuel usage
Service Vehicle Regularly: Proper maintenance prevents poor fuel economy related to dirty air filters, old spark plugs or low fluid levels.
Use Cruise Control: Maintaining a constant speed over long distances often saves gas.
Avoid Heavy Loads: Remove the unnecessary load from your vehicle and pack lightly for long trips.
Avoid Long Idles: If you anticipate being stopped for more than 1 minute, shut off the car. Restarting the car uses less fuel than letting it idle for this time.
Purchase a Fuel Efficient Vehicle: When buying a new vehicle examine the vehicle's rated fuel efficiency. Usually choosing a small vehicle with a manual transmission will provide you with great fuel economy. Also diesel vehicles tend to be more fuel-efficient. Recent technological improvements behind the manufacture of diesel engines, have yielded a more efficient and environmentally friendly fuel. Improvements have also been made to the processing of diesel for more efficient combustion.
Avoid filling gas tank to top. Overfilling results in sloshing over and out of tank. Never fill gas past the first "click" nozzle, if nozzle is automatic.
Buy Gasolene during the coolest time of day: early morning or late evening is best. During this time, gasoline is densest. Gas pumps measure volumes of gasoline, not densities of fuel concentration and you are charged by the "volume of measurement".
Park your car so that you can later begin to travel in forward gear; avoid reverse gear manoeuvres to save gas.
Think ahead when approaching hills. If you accelerate, do it before you reach the hill, not while you are on it.
Use the correct grade of Fuel: You can improve your gas mileage by 1-2 percent 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 1-2 percent. Also, look for motor oil that says "Energy Conserving" on the API performance symbol to be sure it contains friction-reducing additives.
Useful Links
http://www.howtoadvice.com/SavingGas
http://cars.about.com/od/helpforcarbuyers/tp/ag_top_fuelsave.htm
http://www.edmunds.com/advice/fueleconomy/articles/106842/article.html
http://www.edmunds.com/advice/fueleconomy/articles/105528/article.html
http://www.edmunds.com/advice/fueleconomy/articles/107265/article.html
http://money.cnn.com/2005/09/01/Autos/tipsandadvice/gas_saving_test/index.htm