Use alternative modes of transportation. Ride public transit, where available. It saves gas and reduces overall air pollution. Ride a bike when you can. Travel at reduced speeds.
Fuel consumption increases drastically with increased speed.
Drive at posted speed limits. And speeding tickets cause insurance premiums to skyrocket. Organize or join a car pool, even if it's only yourself and another. You will cut your travel expenses in half, or more. Don't forget to use your highest gear, or overdrive, when driving on the open highway.