A nervous or aggressive driving style, braking and accelerating constantly, increases fuel consumption unnecessarily.
Staying too close to the vehicle in front is hard on both your engine and your brakes, particularly in the city. Driving at high speeds pushes up fuel consumption considerably.
Wherever possible, drive at a steady speed and keep your distance from the cars in front of you. If your car has cruise control or a speed limiter, use it whenever you can to keep your car at a stable speed.
Do not brake at the last minute. Use your engine brake whenever possible and slow down earlier. To anticipate the traffic environment around you, look ahead. By driving at a moderate speed, you will avoid wasting time as well as consuming far less fuel.
In short, adopt a smooth driving style to save money and consume less fuel.