One useful thing to understand is that a car which is already moving, for example driving a certain speed on the high way, consumes a lot less fuel than a car which is constantly starting and stopping in town. This is simply due to physics whereby it takes less energy to move an object which is already in motion than it is to get a stationary object to move.
But what does this mean for us, the drivers? This means that smoother actions are much more efficient in terms of fuel savings than rapid acceleration or rapid breaking. Hitting the gas pedal to the maximum may feel great, but it burns a lot of fuel. Starting up smoother would be the better choice in this case.
Another factor which immediately raises fuel consumption by something like 1 litre is the moment you switch on your air conditioning. Of course in some climates it is very difficult to be without one, however, there is a distinct and clear increase to the fuel consumption due to this. Try to find a healthy balance.
Also, related to the air conditioner, it is much easier to cool down a car which was parked in the shade than a car which was parked under the sun. So just choosing a correct parking spot can reduce your fuel consumption.
Another simple rule from physics is that it takes more energy to move something that is heavier compared to something that is lighter. If you have ever tried moving furniture in your house you definitely know this. When speaking about the car this means that lighter loads are better for lower fuel consumption. This, however, does not mean only your luggage. Filling up only half the tank with fuel is already a lot less weight than filling up the whole tank.
When you are waiting for someone in the car, you could just turn it off. Although an idling car does not use very much fuel, it still does, especially if the air conditioning is on. Anyone who is driving a hybrid car can often find this out when the battery finishes and the car starts to use petrol.
One of the largest factors influencing your fuel consumption is your open windows. This is because a moving car with open windows has much higher resistance due to the airflow and it is that much harder to move the car forward. You can maybe relate to this when you think about walking with an open umbrella against the wind – it is that much harder to push forward and you use a lot more energy. So if possible try close your windows and use the car ventilation or even the air conditioning as the open windows have a greater effect than the use of the AC, especially at higher speeds.
Lastly, when your tires are not inflated more of the rubber gets into contact with the street and this increases the resistance. When you inflate your tires to the pressure specified in your car manual you achieve the most efficient resistance and this will reduce your fuel consumption. You may remember that pushing a heavy object may be impossible but if you lift it on pieces of wood it becomes much easier to push it as less of the object is touching the floor and therefore there is less resistance.