Keep windows closed when traveling at highway speeds. Open windows cause aerodynamic drag. But, operating the air conditioner on the maximum level can reduce your mpg by 5% to 25%, compared to not using it. Also, try to park your car in the shade so you won't have to keep the AC working as hard. Properly inflated tires are safer, lasts longer, and improve your gas mileage by more than 3% per tire. Slow down! Although vehicles reach their optimal fuel economy at different speeds, gas mileage usually decreases over 60 mph.  Try to drive at a constant speed—both acceleration and deceleration waste fuel.  Use cruise control when possible. The car's cruise control system's minor, more precise adjustments will keep your speed constant and save you fuel. Wax your car and keep it clean. This will reduce aerodynamic drag, thus providing better mileage. A clean air filter can improve gas mileage by as much as10%. Perform routine maintenance.