First, Simply Drive Safely
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% which equivalent in gasoline savings to $0.18–$1.19/gallon

Observe the Speed Limit  (New Information)  While each vehicle reaches its optimal fuel economy at a different speed (or range of speeds), gas mileage usually decreases rapidly at speeds above 50 mph.  You can assume that each 5 mph you drive over 50 mph is like paying an additional $0.25 per gallon for gas.  Observing the speed limit is also safer.  Fuel Economy Benefit:  7-14% which is equivalent in gasoline savings to $0.25-$0.51/gallon

Remove Excess Weight  Avoid keeping unnecessary items in your vehicle, especially heavy ones. An extra 100 pounds in your vehicle could reduce your MPG by up to 2 percent. The reduction is based on the percentage of extra weight relative to the vehicle's weight and affects smaller vehicles more than larger ones.  Fuel Economy Benefit:  1-2%/100 lbs which equals $0.04-$0.07/gallon.

Avoid Excessive Idling  Idling can use a quarter to a half gallon of fuel per hour, depending on engine size and air conditioner (AC) use. Turn off your engine when your vehicle is parked. It only takes a few seconds worth of fuel to restart your vehicle. Turning your engine on and off excessively, however, may increase starter wear.  FUEL SAVINGS:  $0.01-$0.03/min with the AC off vs. $0.02-$0.04/min with the AC on.

Using cruise control on the highway helps you maintain a constant speed and, in most cases, will save gas.