Stop speeding – Reducing your speed to 55 mph from 70 mph could increase your fuel efficiency by 23 percent. Don’t have a lead foot – Avoiding rapid acceleration and sudden starts can improve gas mileage by more than 5 percent. Too much junk in the trunk – It’s a known fact that excess weight in your car causes the engine to work harder, wasting more gas. Carpool or use public transportation – This goes without saying ...