Choose the appropriate speed

On the highway, one litre per 100 km can be spared when you drive 10 to 15 km/h less than usual. There is hardly any time-profit by driving faster, because from 70 km/h the impact of air resistance increases exponentially. Maintaining a steady speed can also reduce fuel consumption.
Beware: safety is most important! Don't put other people in danger by driving at an inappropriate speed. When you drive too slowly, your savings will be counteracted because the traffic behind you needs to slow down and then accelerate again to pass you by.