• 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.
• 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.
• 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%. The reduction is based on the percentage of extra weight relative to the vehicle's weight and affects smaller vehicles more than larger ones.
• Avoid Excessive Idling: Idling gets 0 miles per gallon. Cars with larger engines typically waste more gas at idle than do cars with smaller engines.
• Use Cruise Control: Using cruise control on the highway helps you maintain a constant speed and, in most cases, will save gas.
• Use Overdrive Gears: When you use overdrive gearing, your car's engine speed goes down. This saves gas and reduces engine wear.

Resources:

AAA Fuel Price Finder

Fueleconomy.gov

Federal Trade Commision

Environmental Protection Agency

Department of Energy

Light-Duty Automotive Technology and Fuel Economy Trends

Green Vehicle Guide

Department of Transportation-National Highway and Traffic Administration's (NHTSA) Corporate Average Fuel Economy (CAFE) Program