From the U.S. Department of Energy come the following sensible Gas Mileage Tips:
Drive Sensibly
Aggressive driving (speeding, rapid acceleration and braking) wastes gas. It can lower your gas mileage by 33 percent at highway speeds and by 5 percent around town. Sensible driving is also safer for you and others, so you may save more than gas money.
Fuel Economy Benefit: 5-33%
Equivalent Gasoline Savings: $0.20-$1.35/gallon
Observe the Speed Limit
While each vehicle reaches its optimal fuel economy at a different speed (or range of speeds), gas mileage usually decreases rapidly at speeds above 60 mph.