Besides having a source of free gas, or converting you car to run partially on water, there are some tips that can certainly help you in your fight at the pump. The following list of tips, if you follow them, will increase fuel economy. You just have to implement them.
1. Check your air filter
A clean air filter is the key to good fuel economy. A dirty air filter restricts the flow of air into the engine, which harms performance and economy. Air filters are easy to check and change; remove the filter and hold it up to the sun. If you can't see light coming through it, you need a new one. I use K&N filters which is cleaned rather than changed; they are much less restrictive (better air flow) than throw-away paper filters, plus they're better for the environment.
2. Get back to nature
Consider shutting off the air conditioner, opening the windows and enjoying the breeze. It may be a tad warmer, but at lower speeds you'll save fuel. That said, at higher speeds the A/C may be more efficient than the wind resistance from open windows and sunroof.
3. Use the correct tires for your vehicle
New wheels and tires may look cool, and they can certainly improve handling. But if they are wider than the stock tires, chances are they'll create more rolling resistance and decrease fuel economy. If you upgrade your wheels and tires, keep the old ones. For long road trips, the stock wheels give a smoother ride and better economy.
4. Drive only when you have to
Not a popular thing to say on a car site, I know, but the fact is that if you can avoid driving, you'll save gas. Take the train, carpool, and consolidate your shopping trips. Walking or biking is good for your wallet and your health. And before you get in your car, always ask yourself: "Is this trip really necessary?"
5. Avoid High Speeds
As your speed increases, your aerodynamic drag increases in an exponential fashion. Driving 62 mph (100 km/h) Vs 75 mph (120 km/h) will reduce fuel consumption by about 15%.
6. Do Not Accelerate or Brake Hard
By anticipating the traffic and applying slow steady acceleration and braking, fuel economy may increase by as much as 20%.
7. Use A/C Sparingly
When the air conditioner is on it puts extra load on the engine forcing more fuel to be used (by about 20%). The defrost position on most vehicles also uses the air conditioner.
8. Keep Windows Closed
Windows open, especially at highway speeds, increase drag and result in decreased fuel economy of up to 10%.
9. Service Vehicle Regularly
Proper maintenance avoids poor fuel economy related to dirty air filters, old spark plugs or low fluid levels.
10. Use Cruise Control.
Maintaining a constant speed over long distances often saves gas. It can save you up to 4 MPG.
11. Avoid Heavy Loads and get the junk out of your trunk.
Remove the sandbags (junk) from your trunk and pack lightly for long trips.
The rule of thumb is, for every extra 100 pounds you lose 1 mpg. Remove the weight and save gas.
12. Avoid Long Idles
If you anticipate being stopped for more than 1 minute, shut off the car. Restarting the car uses less fuel than letting it idle for this time.