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A heavy car needs more gas. So put your vehicle on a diet to get rid of excess weight. Losing 100 pounds can reduce your MPG up to 2%. Keep emergency essentials like a spare tire, first aid kit and flares, but decide if you really need to haul your golf bag to the mall.

Aggressive driving–speeding, rapid acceleration and braking–burns gas at a faster rate than keeping the car at a steady pace. Speeding can lower your gas mileage by 33% on the highway and 5% in the city, not to mention what it can cost in tickets. Slower driving affords you more reaction time to avoid accidents; it's a sound move all-around.

A well-maintained car is a gas-efficient car, so keep your engine properly tuned. Take it in for regular tune-ups–fixing a car that has failed an emissions test improves gas mileage an average of 4%.

Saggy, under-inflated tires are not only dangerous to drive on, they're dangerous to your cash flow. You can improve gas mileage by around 3% by keeping your tires inflated to the correct pressure. Check tire pressure every month and always in the morning since readings on driven tires are less accurate.

Replacing a clogged air filter can improve your car's gas mileage by as much as 10%. It can also protect your engine from outside impurities, saving you money in potential repairs.

The best way to save money and improve gas mileage is to drive a more fuel efficient vehicle. It's no secret that compact cars will get more miles to the gallon than hulking SUVs. Assuming 15,000 miles of driving annually and a fuel cost of $4.00 a gallon (sorry, get used to it), the difference between a car that gets 20 MPG and 30 MPG comes to $1,000 per year. That's $5,000 in fuel costs over five years and $10,000 over the life of the car! So, when you're choosing between a hybrid and a Hummer, choose wisely.