Tips improving fuel efficiency

Keep your car well maintained
Keeping the engine properly tuned can improve it's fuel efficiency. Fixing a faulty oxygen sensor can improve your efficiency by up to 40%.

Check for correct tire pressue
Keep your tires inflated to the proper tire pressure. Proper inflated tires are safer and last longer. Your engine has to work harder with under-inflated tires as the rolling resistance is greater.

Straighten out, drive right
Poor wheel alignment makes tires wear out more quickly and forces your engine to work harder, reducing the fuel efficiency.

Check your tank cap
Fixing and replacing and broken cap will not only improve the fuel efficiency it will also help the environment.

Loose extra weight
For each additional 100 pounds loaded into your car, you lose 1% to 2% in fuel efficiency. Empty your trunk and save money.

Don't just sit and idle
If you need to stop the for more than 30 seconds, turn off the engine. And don't bother "warming up" your car before driving -- it's not necessary.

Check your driving habits
Aggressive driving (speeding, rapid acceleration and braking) wastes gas. Sensible driving is also safer for you and others, so you may save more than gas money.

More on Saving Tips

Wikipedia’s Fuel economy-maximizing behaviors

U.S. Deparment of Energy

Fuel Economy Blog