Bunch of tips for upping gas mileage and sticking it to the man:
1) This one is so simple, it's almost stupid. Keep track of your mileage. It's surprising how much better you'll drive when you realize what you're spending. Just keep track of the miles since your last fillup and divide by the gallons of the next fillup. Make it a game and try to beat your high score. Make it a competition and try to beat your friend's best scores (or percent improvement).
2) Don't speed. It's cliche but true. Driving 55 uses 20% less gas than 70. So slowing down should at least get you 10%.
3) Get that crap out of your car. Every 100 pounds you take out is a 1% increase. So take those boxes of books out of the back seat. Dump that dead body wrapped in the rug out of your trunk. Lose some weight. Whatever you have to do, lighten the load.
4) Get that crap off your car. Yes that bike/luggage/ski rack may weigh your car down a bit. But what it's really doing is killing your car's aerodynamics because they cause a lot of drag. If you don't need them, take them off.
5) Brake better. Braking eats your gas mileage because you lose speed you spent gas building up, and you have to burn gas to speed up again. Just leaving a bigger gap between the car in front of you gives you more time to coast or brake less. And if you're coming up to a red light, go ahead and just take your foot of the gas so you don't have to brake so hard (and maybe not have to stop at all when the light changes).
6) Keep those tires inflated. Not only is it safer, but it can save you 1% n mileage.
7) Cruise control is your friend. Moving up and down in speed eats gas. Cruise control can keep you at a steady pace, and improve engine efficiency. But it's best used on a flat highway. Don't use it in-town, or on a hilly road (since cruise control will accelerate up a hill and brake going down, both of which waste gas).
8) Don't fill up until you need to. Gas weighs a lot, and the less gas you have in your tank, the less gas you have to burn to move your car. So wait until you're below a quarter tank. Just don't risk running out.
9) Low RPM shifting (manual transmissions). Manual transmissions tend to get better mileage because you can control when shifting happens. Shifting up early and shifting down late can save gas. (In automatic transmission cars, always drive with the overdrive gear on since it's more efficient.)
10) Shifting into neutral (automatic transmissions). When idling, your car gets 0 mpg. But it uses less gas when idling in neutral instead of drive. This is because the engine doesn't need to work as hard. Neutral also gives your transmission a chance to cool down, which can reduce wear and tear. BIG WARNINGS: Only do this when you'll be idling for a long time (like at a long red or waiting for a train to pass). Frequent shifting can actually add more wear and tear than neutral would save. You'll end up spending more in transmission repair than saving in gas. Also, never coast downhill in neutral. It'll eat up your brakes and is usually illegal.
11) Windows or air conditioner? The best thing to do is keep your windows up and not use the AC. But that's rarely possible. Your car's drag increases when the windows are down. But the AC eats gas too. Once you get over 40, the drag outweighs the AC. So the rule of thumb is, windows down in-town, AC on the highway.
12) Enjoy the slipstream. But don't tailgate a semi-truck! Because you don't need to. Driving behind a semi not only saves gas because you're driving slower, but even 150 feet behind a semi you can cut your wind drag by 10-20%.
13) Purely a money saving tip, but get a cash back credit card and only buy gas with it. Then pay the card off before you get any finance charges. This means your credit card becomes an ATM, and you'll get money back. (I get 1% back for 3 quarters of the year, and 5% during the other quarter.) And you'll boost your credit rating too.