Take care of your car and it will take care of you. Just as an athlete can't perform at top efficiency while running at high altitude in bad shoes, a suffocating car on improperly inflated tires will gulp gas like Gatorade. In fact, for every 1-pound pressure drop in all four tires, you're losing 0.4 percent fuel efficiency [source: Car Talk].
So get your vehicle serviced regularly. Fix mileage-killing problems like sticky brake calipers, low transmission fluid or a broken thermostat ASAP. Find your proper tire pressure in your driver's manual or look in your driver's side door jamb for the tire and loading information tag. Note that the ideal pressures might differ from front to rear, and ignore the number on the tire's sidewall -- that's a maximum pressure listed for safety purposes. Learn the proper technique for measuring inflation and consider investing in valve stem caps with built-in pressure indicators; you could cut fuel consumption by 3.3 percent [sources: Allen; Car Talk; DOE; GSA; Wiesenfelder].
Last but not least, buy the right motor oil. Pouring in the manufacturer's recommended grade can mean a 1-2 percent efficiency boost, whereas going with whatever's on special that week can lose you just as much. Replacing a clogged air filter will boost fuel efficiency on older cars, but not on modern fuel-injected vehicles [source: Car Talk; DOE].