Check List:
1. Keep track of your mileage every time you fill up your tank. If it changes, find out why.
2. Don't speed so you burn your gas more efficiently.
3. Don't carry unnecessary weight in the car.
4. Make sure your tires are inflated to the proper pressure.
5. Change your motor oil frequently.
6. Use gas of the proper octane level.
7. Use your air conditioner sparingly.
8. Keep an even speed. Use cruise control.
9. Drive at 55mph to save gas.
10. Choose route with fewest stops
11. Do all your errands at once. Less trips, less gas.
12. Use highways instead of city streets.
* The bigger the car and the engine, the more gas you will use. Consider your gas budget when buying a new car.

Watch Your Speed
Drive slower -The drag force at 70 mph (113 kph) is about double that at 50 mph (81 kph). So, keeping your speed down can increase your mileage significantly. Try to keep your driving speed at or below 60 mph. Driving faster than 60 mph can significantly decrease your gas mileage. While this may be tough for some of you speed demons out there, it helps to think about this fact: You will end up paying an extra $0.20 per gallon for every 5 mph above 60 that you drive. Add that up and you've got a pretty little chunk of change that you're wasting in order to get somewhere a little bit faster (not to mention all those speeding tickets).

Avoid Sudden Stops
If you stop quickly, the brakes on the car will do most of the work of slowing the car down, and that energy will be wasted.
If you aren’t driving that way now, you probably aren’t getting the best gas mileage possible out of your present vehicle. A lot of your gasoline consumption relies on you…no matter what type of car you’re driving!

Reduce Excess Weight
The heavier your car is (and the stuff in it), the more work that your engine needs to do in order to move it forward. The more work that your engine has to do, the more gas it needs to use in order to do it. This is why a good deal of excess weight in your car can reduce the gas mileage that you get (and why larger cars often get worse gas mileage than smaller ones). Go through your car and remove any unnecessary items that you don't need (power tools, skis, boxes, etc.). The lighter your car is, the better gas mileage you'll get.

Avoid Idling
Besides getting you nowhere, idling in your car can be a serious waste of gas and fuel efficiency (basically 0 mph). When you idle, your engine is still using gas even though your car isn't moving. While some amount of idling is necessary, such as at red lights and in traffic congestion, the rest of the time you should try to idle as little as possible. Whether you're waiting in line at the drive-thru or sitting at the curbside pickup at the airport waiting for a friend, if you anticipate that you won't be moving for an extended period of time - go ahead and turn off your car.

Maintain Constant Speed
From hard braking and quick accelerating to jerky steering and speeding, erratic driving can cause a serious drop in your fuel efficiency. Try to stay calm when you drive. Give yourself enough time to break gradually at stop lights. Don't slam on the accelerator when the light turns green. And in general, try to drive defensively rather than aggressively. It'll end up saving you money (and reduce the chances of you having an accident).

Use Overdrive and Cruise Control
These two functions are found on most cars and can be effective tools for increasing fuel efficiency and saving gas. Cruise control works by automatically maintaining the speed at which your car is going. Keeping your car at a steady speed for extended periods of time (like on road trips) can help save gas. Overdrive gears work by reducing the speed of your engine - which can also save you a good deal of gas. While these two functions shouldn't be used all the time, they can help your gas mileage in certain situations.

Car Maintenance
Keeping your car well maintained and in good working condition is another way that you can ensure you are getting the best gas mileage possible out of your vehicle. While regular service and maintenance are important parts of keeping your car running properly (and preventing costly repairs), they can also save you money by raising your car's fuel efficiency.

Monitor Tire Pressure
Low tire pressure can decrease fuel efficiency
One simple thing that you can do in order to improve fuel efficiency is to always keep your tires inflated to the correct level. Tires that are low on air are harder to roll and require more work from your engine and more gas consumption. Make sure that you check your car's tire pressure every time you fuel up (most gas stations have an air pump that customers can use). If you're unsure about how much air to put in your tires, check the owner's manual to find out the recommended psi for your specific vehicle.

Replace Your Air Filter
Another part of your car that can effect gas mileage is the air filter. A clogged air filter can greatly reduce the amount of oxygen that your engine can use for burning fuel. This lack of oxygen can result in an inefficient fuel mixture and a decrease in engine power (all leading to lower gas mileage). Besides improving fuel efficiency, replacing your air filter can also help improve performance. Check your owner's manual to see how often they recommend changing filters (usually every 15,000 miles).

Change Your Oil
While you've probably been told that changing your oil every 3,000 miles can help keep your engine clean and problem free, you may not know that it can also help improve your gas mileage. When getting your oil changed, make sure that you always choose the recommended grade of motor oil for your specific vehicle (you can find this information in your owner's manual).

Use the Right Octane Level
When choosing which octane level of gas to buy at the pump, always go with the manufacturer's recommended level. If your car runs best on regular octane gas, then there is no reason for you to buy higher grade fuel (basically a waste of money). But if your car requires higher octane fuel, lower octane gas can damage your engine and decrease your car's fuel efficiency.

Other Gas Saving Tips
Here are some other tips that you can use to help improve your gas mileage (and save money!)
* Avoid using your air conditioning.
* Keep your windows closed. Having the windows down causes wind drag on your car which makes the engine work harder to keep up the same speed, using more gas.
* External vehicle accessories like ski racks and luggage containers can lower the aerodynamics of your car and make your engine work harder. Unless you are using them - take them off and put them in storage.
* Plan your driving route. Since starting your car when the engine is cold for a few short trips can often use twice as much fuel as one continuous trip (traveling the same distance, try planning your driving route so that you can take care of as many errands as possible with as few stops as possible.