I'll add to Tony's just a bit on how to maximize driving fuel efficiency in your car.
Required:
- Ease up off the pedal, don't jackrabit, and obey the speed limit.
- Maintain a good Tire pressure (32 to 35 PSI) all around.
- Empty trunk and car of USELESS or HEAVY items (the more you remove, the better for your fuel mileage)
- Run fuel additives (injector cleaner, etc.)
- Replace dirty air filter with a clean one (or open-air with heatshield)
Optional:
- Give your UIM/LIM a good
cleaning
- Remove your spare tire (it's optional if you don't feel you need it)
- Tune your car, change plugs/plug wires, etc.
- Use 5w20 full synethtic oil in your car on your next oil change.
- Hit the gym maybe? Drop 30 to 40 pounds? (haha)
This is just in general, but I found doing the required and some of the optional stuff results in you just squeaking that extra little but out of your tank. Hope that helps, keep in mind this is in the long run.