Tune up to give me better gas mileage

Basically you are going to want to do all the basic maintenance sort of things.

1. Change engine air filter
2. Change engine oil and oil filter
3. Change spark plugs
4. Make sure your tires are filled to tired specifications
5. Remove all unnecessary weight
6. Make sure all the other accessory pulleys are spinning and are not seized
7. Change your driving style, so you are easy on the throttle and brakes.

Those are the seven top tips I can think of to get the most mileage out of your vehicle.