Let's start with the most obvious . . . drive less. Walk, bike, use public transit, and carpool when possible. Check with your local public transportation authorities; they often have carpooling information as well as their regular services. If you own more than one car, choose the one that gets the best gas mileage whenever possible. Make the most of each car trip by combining as many errands as you can.
How you maintain your car can have a significant impact on gas mileage. Make sure to get regular tune-ups. Stick with the recommended maintenance schedule found in your owner's manual. Keep tires properly inflated (again, check your owner's manual) and aligned. You can even improve your car's gas mileage by using the manufacturer's recommended grade of motor oil. Selecting oil labeled "energy conserving" can also help.
When it's time to gas up make sure to fill the tank so you don't waste time, money, and fuel driving back to the service station for another small purchase. Never top off the gas tank though. Once the nozzle clicks off the first time the gas you're paying for is not going into your tank. Waiting until you have just a quarter tank (but no lower) can improve your gas mileage because you are carrying a lighter fuel load.
The way you drive is also important. For optimal gas mileage drive at a constant speed and avoid quick accelerations and hard braking. When there is little traffic use cruise control. You can also improve your gas mileage by 15% if you drive at 55 mph instead of 65 mph. When it comes to manual transmissions the lower the shift speed the better the gas mileage so remember to shift up early and shift down late.
Avoid idling. Turn off the engine whenever you will not be moving for a minute or more. If you're stuck in traffic or in another scenario where you can't turn off the engine, shift into neutral instead.
Keep your car light to boost fuel efficiency. Take out any unneeded items from the trunk and reduce drag by carrying items inside the car rather than on a roof rack.
On hot days seek out parking spots in the shade to reduce gas evaporation as well as your need for air conditioning. Investing in a good windshield shade will help keep your car cool which also reduces your need for AC. If you have a garage, make sure to use it to park your car. Parking in your garage helps your car stay warm in the winter and cool in the summer, reducing your need for heat, defrost, and AC. When you do use the heat or air conditioning remember to turn it off 5 minutes before you reach your destination.
If you're in the market for a new car, get only the options you really need. Optional features, such as four-wheel drive, can significantly decrease your gas mileage. Manual transmissions have better fuel economy than automatic transmissions. Get only the size of car you truly need since the bigger the engine the lower the fuel efficiency. Decide on your required model size and compare the gas mileage of cars in that category at fueleconomy.gov – the official U.S. government source for fuel economy information. Consumer Reports released its list of the most fuel-efficient cars tested just this past February. If you're considering a hybrid, compare the stats and features of available hybrids at Hybridcenter.org.