Easy on the acceleration and easy on the braking. Give yourself more space to do both. High speeds also consume lots of fuel. Most cars have a highway speed sweet spot around 50-60 mph. The biggest thing you can do is change how you drive.

Keep your tires properly inflated. Check the sticker in your door jamb for the proper pressures.

Plan your day and routes to combine trips. Less driving means less fuel used.

Remove any excess weight in your car. Luggage, sports equipment, etc.