You can do some work on your car
1. Make sure the tires are properly inflated (between the # on the car and the tire)
2. Get a full tune up
3. Change your oil to a lighter weight. (5w30 rather than 10w30)
4. Drive slower (55-60 on most cars is the best range for fuel effeiency)
5. Use your crusie control when safe
6. Do not use your AC.
7. Do not roll down your windows
8. Make sure you purchase the proper fuel. (unless you have a sports car or luxury car, you do not need 92 fuel. Check with your owners manual to confirm)
9. Make your car go on a diet- remove bowling balls, spare books, extra floormats, etc)
10. Accelerate moderately
Just a few tips off the top of my head.