There are a number of things you can do to your vehicle to improve your gas mileage.

For one, reduce your speed if at all possible on the highway. The ideal speed range for the best MPG is between 30 and 60 miles per hour. It peaks at around 55, but it's better to obey the traffic laws if you're in town! A ticket can set you back far more than anything you might have saved in gas. However, your mileage drops almost exponentially after 60 MPH, so try to stay around that speed on the highway.

Be less aggressive. If you find yourself using your breaks a lot, then you're either driving too fast or too close to the vehicle in front of you. Also, this reduces your break linings and wears at your rotors, needing break repairs more often (and often they are costlier too). If you take off suddenly from a stopped position, that sucks a lot of gas to your engine. And of course, if you're speeding, we've already covered that, but a lot more traffic signals are synchronized, so you may not be gaining anything by going faster (and subsequently, having to break again and lose all that kinetic energy to heat, and reducing your brake pad thickness).

There's a myth out there that starting your vehicle uses more gas than idling. You may have also heard the commercials that tell you that starting your engine is the worst thing you could do for it. Well, the first part isn't true, and the second part is only partially true. Idling wastes gas, period. If you're going to be somewhere for a while, and you don't need the air conditioning (open your windows) or heat, then you're better off shutting the engine off (unless you fear not being able to start it again). Electric generators use quite a bit of gas even while it doesn't have a load, and those are small engines. Your vehicle's engine is quite a bit larger. Don't run your engine when it's not needed for any more than a minute or two. You know the lights you typically get stopped at. If it just turned red, and you know it takes 3 or more minutes before you can begin pressing the accelerator again, then you might as well shut it off. If the drive thru isn't moving, either go inside or shut off your engine.

As far as it being damaging to start your vehicle, that's really only true during cold starts, where the oil has drained back into the pan. This takes a while, so don't worry about this unless it's more than 30 minutes, and by then, you're probably already going crazy being stuck in your vehicle going nowhere!

Inflate your tires and keep them aligned. Underinflated tires makes your engine work harder. Try to keep them near the maximum pressure recommended by the manufacturer. Malaligned tires also make your engine work harder. Both underinflation and malaligned tires are also bad for your tire's tread and overall health, costing you more money in two different ways.

With the gas stations limiting the amount of gas you can purchase at a time, and with gas prices being so expensive, this may not be an issue for you, but don't overfill your vehicle's tank. Once that pump stops the first time, don't give it a go five or six more times. Typically, this extra gas either gets absorbed by the vapor recovery system, or gets spilled out onto the road, which is bad for the environment, your vehicle's vapor recovery system, the gas station's vapor recovery system, and your wallet. Also, your fuel tank needs room to breathe. If you overfill your tank, it'll have to go somewhere during the expansion of liquids exposed to the environmental heat (gas, in underground tanks, is cooler until it hits a Southern state's warmer atmosphere). Did you know that when you over fill your tank, you may be giving the gas station their gas back? To find out more, read this article from the EPA: http://www.epa.gov/donttopoff

Do you have an overdrive transmission? This is typically turned on and off by a button on the gear shifter. When it's turned off, there's usually a light that's turned on in your indicator panel (usually somewhere near your speedometer). If you're not using overdrive on long trips, you're probably losing tons of efficiency and MPG. This last gear (overdrive gear) is the most efficient gear for going higher speeds (again, not over 60 MPH). However, according to a Wikipedia article, it's better not to use overdrive for normal around town driving.

Whenever you're on a long trip, it's best to make full use of the cruise control. Make sure you learn how to use this tool before you use it, however. It will make driving more comfortable, and will save gas because your engine maintains (or tries to maintain) a constant speed. I find in hilly regions, this doesn't work too well. It's not the speed you're trying to maintain to save gas, rather, the revolutions your engine makes. Cruise control handles this by maintaining its speed. However, in a section of Interstate that has slopes and valleys, maintaining the speed AND the revolutions becomes couter productive, and the cruise control typically drops into a lower gear to try to maintain that speed, increasing the engine's revs, which is what we don't want.

But, overall, using cruise control is more efficient than humans in normal situations.

If you're carrying around more than 100 pounds of extra weight (in your vehicle) that can be stored in your garage or elsewhere, you're wasting gas on it. You'll have to decide if not having it in your vehicle is an option, however. If it's your snow tires, you can probably safely store these in your garage. If you carry large amounts of water for emergencies, unless you're going outside of a populated area, you can probably get rid of this also.

When was the last time you checked or replaced your air filter? If you can't remember, it's probably a good time to do so. Engines need air, and lots of it. That's why high performance cars have forced air (ram air) induction systems, to force more air into the engine. However, don't go modifying your car's air intake with electronic forced air induction systems (unless you really want to, and you really know what you're doing). Changing your dirty air filter will suffice. If you want, and I recommend this, you can drop some extra coin and get a performance air filter. They allow more air in than a regular air filter, and they cost less over time because they are typically cleanable and reusable. Don't do anything that will void your manufacturer's warranty, however.

Keep your car tuned up, and have your oxygen sensor checked. Replacing the oxygen sensor can save you tons of cash if it's faulty. You'll probably know if your oxygen sensor becomes faulty, however. Well, you may not know that its your oxygen sensor, but you'll know something's wrong! Not only can your gas consumption go through the roof, but your car will probably complain in other noisy ways. To replace it, it costs roughly $70 at your nearest auto parts store, and it's apparently user servicable (not that I would begin to know how to do this on my own vehicle). Let your nearest, friendliest, honest auto mechanic take a look and give you an estimate (now that you know how much the part costs).

If you treat your car right, it will treat you (and your wallet) right. Keep it maintained and in top condition, and it'll save you money in lots of ways in the long run.