Racing away from green lights
When the light turns green, you don't have to take off as quickly as possible.
Racing up to red lights
When you're driving down the street, and you see a light red light or stop sign up ahead, you should lay off the gas sooner rather than later.
Confusing the highway with a speedway
Even if it doesn't involve hard acceleration, speeding wastes gas. The faster you go, the more air your vehicle has to push out of the way.
Tailgating is a bad move for many reasons. First of all, it's unsafe... and tailgating wastes gas. Every time the driver ahead taps his brakes, you have to slow down even more than he did. Then you accelerate again wasting gas.
Driving standing still
You've probably heard that it takes more gas to restart a car than to let it run. But with modern engines it takes very little extra gas to restart a car once it's warmed up. Idling, meanwhile, burns about a half-mile worth of gas every minute.
For really short trips, take advantage of the opportunity to get some exercise. Try walking to the store instead of driving. You can save gas and burn a few calories instead.