One of the easiest and cheapest ways to gain more fuel mileage is by replacing your vehicles air filter often. Check the element at every oil change service and replace it when you can not see light through it. If light has a hard time getting through, then air will also have a hard time getting through. Other vehicles are similar and should be maintained in the same way. Don't forget to reset the maintenance indicator light once your oil is changed and your air filter is checked or changed.
How do I Replace the Air Filter On my '94 Saturn ?
Fig. 1: Exploded view of the air filter components — SOHC engine