Fill your tank in the morning. Don’t drive aggressively. Fill up when you have half a tank. Change to the highest gear rather than driving in the lowest gear. Service your car regularly. Don't over rev your car. Don't be hard on your brakes or accelerator. Ensure your tyre pressure is correct. Shop around for diesel prices. Travel at a constant speed where possible. It is more economical to use the aircon than driving with the windows open.