1. Use high gear to drive moderately fast but never be too fast as you will need to achieve high rpm as you get faster.
2. Keep your rpm lowest possible at around 2000rpm. When your rpm increases from 2000 to 3000, the fuel consumption increases exponentially as compared to increase from 1000 to 2000.
3. Switch off the air-cond. A typical car air-cond consumes at least 500W, which is the roughly the same power to move a car. In a Mythbuster episode, they have proven that opening the windows for ventilation does not cause much air drag. So it’s better to open the windows a little bit rather than switching on the air-cond.
4. Switch gear to neutral as frequent as possible. This is because getting your tyres engaged to the engine produces so much friction that you can feel it yourself.
5. Accelerate a little for momentum before going up hill to keep rpm low when climbing hills.
6. Keep acceleration low. Do not accelerate abruptly as energy is wasted somewhere in the clutch of the car.
7. In another Mythbuster episode, they have proven you can save much fuel by following a vehicle as near as possible, because there is a suction behind these cars and it is better a truck or big car with big air turbulence. By doing so, you remove 80% friction, not 80% fuel consumption as claimed by Terence R.
8. Inflate your tyres immediately. Soft tyres or deflated tyres consumes so much power that you can feel the friction. If you had experience with cycling, you would know deflated tyres strain your leg muscles so much.
9. Avoid stops/slowing downs as they waste fuel energy. Instead, release the fuel pedal to let the car slows down over the distance rather than braking the car.
F1 driver, haha.