From saving gas to lowering the cost of routine maintenance, a few simple habits keep costs in check.

For most Americans, driving is a necessity of life. But as budgets tighten and fuel prices fluctuate, many people are looking for ways to trim the price of driving. When buying a car, opting for a used vehicle can cut the cost of ownership from the very first day. The price is normally thousands less than for the same car new. In addition, a lower price means less sales tax, less money to finance the purchase, and a lower premium on any collision and comprehensive insurance. To get the best fuel economy, choosing a four-cylinder engine rather than a V6, or a V6 rather than a V8, is usually the way to go. Likewise, small, light cars tend to be more miserly with fuel than are larger vehicles. To compare specific models, go to the Environmental Protection Agency's web site at www.fueleconomy.gov. Once you've bought a vehicle, you can still go farther for less money if you follow a few common-sense practices. To aid your efforts, keep a notebook in the car, and for a few months write down everything you spend on driving--fuel, maintenance, tolls, and parking. Knowing where the money goes is the best guide to finding significant places to save. Here are some other tips.

NO LOITERING

Think of it this way: while idling, your car is getting zero miles per gallon (mpg). Don't let the engine run at idle for any longer than necessary. After starting the car in the morning, begin driving right away; don't let it sit and "warm up" for several minutes. An engine actually warms up faster while driving. With most gasoline engines, it's more efficient to turn off the engine rather than idle for 30 seconds or longer. Think about going into a fast-food restaurant rather than waiting in a long line for the drive-through window.

EASY DOES IT

Driving smoothly and steadily makes the best use of your fuel. If you can, avoid hard acceleration or braking. When you move out from a standstill, bring the car up to speed briskly but not abruptly. You want to get up to cruising speed without straining, and then stay there. Once up to speed, maintain a steady pace in top gear. Varying your speed a lot wastes fuel. According to the EPA, the most fuel-efficient speeds are between about 25 and 60 mph. Smooth acceleration, cornering, and braking not only save fuel, but extend the life of the engine, transmission, and brakes.

DON'T BE A DRAG

At highway speeds, over 50 percent of engine power goes to overcoming aerodynamic drag. Try not to add to the drag by carrying things on top of your vehicle. A loaded roof rack can decrease a car's fuel economy by 5 percent. Even driving with empty ski racks wastes gas. In addition, if you have air conditioning, don't ride with your windows open on the highway; this also disturbs the outside airflow and creates extra drag.

STAY WARM

An engine runs most inefficiently when it's cold. It not only uses more fuel during this period, but also creates the dirtiest emissions and suffers the most wear. Avoid lots of short, separate trips--and unnecessary cold starts--by combining as many errands as possible into one trip.

GETTING REGULAR

If your car specifies regular fuel, don't buy premium in the mistaken belief that your engine will run better. Using premium fuel in those circumstances is like buying bigger sneakers in the hope they'll help you run faster. Most cars are designed to run just fine on regular gasoline. Furthermore, many cars that recommend premium fuel also run well on regular. You can check with your dealership as to whether your engine is designed to handle either grade. If so, try a tankful or two of regular. If you see no difference in mileage or engine performance, stick with it.

BUY BARGIN FUEL AND OIL

Off-brand gasoline is most often identical to what is sold at franchised gas stations. Shop for the cheapest. Likewise, look for promotional sales at quick-lube shops. Just make sure the shop uses the correct service-grade and viscosity oil for your car. Following your car's recommended oil-change intervals is sufficient, which for most cars driven under normal conditions is 7,500 miles. While oil companies and lube shops may recommend changing oil every 3,000 miles, this can be an unnecessary expense. You can change the oil yourself-typically for $10 or so for oil and a filter. But since a commercial oil change routinely costs $20 or so, you have to weigh whether the savings is worth the time and effort, plus the hassle of safely disposing of your used oil.

STAY TUNED

The EPA mileage that's posted on new-car window stickers is based on a well-tuned and properly maintained vehicle. Running a car in subpar condition can lower that figure dramatically. A poorly tuned engine can cut gas mileage by 10 to 20 percent. Modern electronically controlled engines don't need the frequent and extensive tune-ups of older cars, but they still need regular maintenance and suffer component failures. A clogged air filter alone can cause up to a 10 percent increase in fuel consumption. Be sure to follow the maintenance schedule in your owner's manual, and act promptly if you sense any unusual sounds, smells, or vibration. . Dealership service departments tend to have the most up-to-date tools, equipment, and experience with your car, so they're the places to go if the problem is a real puzzle. But any good mechanic can perform routine service and repair, and independent shops or service stations are often cheaper than using the service department at a dealership.

ROUTINE ISN'T ALWAYS THE SAME

Before you have routine maintenance performed on your vehicle, call around for the best price. Even different dealerships of the same brand can charge varying amounts for the same service interval. Routine maintenance can also be done by independent shops, which are generally less expensive than dealerships. Just keep good records in case you later have a warranty claim. Check in your owner's manual to make sure that the price includes all necessary service, but doesn't add in unnecessary extras. If you're handy, you can also do simple maintenance yourself; just keep all receipts as proof of what parts or fluids were used and when.

WATCH THE TIRES

Keep your tires properly inflated. Underinflated tires require more energy to roll, which not only wastes fuel but wears the tires faster. According to the EPA, one tire that's underinflated by only two psi will result in a 1 percent increase in fuel consumption. Underinflated tires can also build up excess heat, which can lead to tire failure. Check tire pressures monthly when the tires are cold. The recommended tire pressures are found on a label inside the car--usually in a doorjamb or inside the glove-box lid.

SHOP FOR INSURANCE

Some insurers charge twice as much as others for the same customer and car. Using the Internet or the Yellow Pages, shop around for the best insurance-rate quotes you can find. You should carry ample liability insurance, but you don't need to splurge much on collision and comprehensive if your car is getting on in years. Once collision and comprehensive premiums reach 10 percent of the car's book value, consider dropping them. Also raise your deductibles to the highest limit you are comfortable with: say $500 or $1,000. Recheck the insurance market for competitive rates every year or two.