Keep your engine in tune. Fixing a car that is out of tune or has failed an emissions test can boost gas mileage by about 4 percent.

So be sure to give your car regular tune-ups. You'll also want to watch out for worn spark plugs. A misfiring spark plug can reduce a car's fuel efficiency by as much as 30 percent.

Fill up with a lower-octane gasoline. Unless your car requires premium gasoline, filling up your car with high-octane fuel is a waste of money. That pricey premium fuel won't boost your car's fuel economy or performance in the least, so skip it.