To minimise fuel consumption you could look at taking a reasonable approach to using the electrical appliances run by your car. This may be done by turning of the appliances which are not in use such as the heated seats or put them on a low setting.
Air conditioning pumps energy from the engine. When it is hot outside, fuel consumption can rise by as much as 25% if you keep the cabin at a low temperature. Use air conditioning wisely and, if you have an automatic system, avoid selecting a temperature that is too cold or more than 4 or 5° degrees lower than the outside temperature. As well as saving fuel, you will avoid "heat shock" when you get into or out of the car.
If your car has been parked in the sun for a long period, start off at a low speed with the air conditioning off and all the windows open to let the heat out. The air conditioning can then take over to maintain the cabin at a constant temperature when the windows are closed.