Don't race to that red light and then peel out when it turns green -- quick braking and accelerating wastes gas. Instead, you can ride out your car's momentum and take advantage of your engine's idle revolutions per minute to save some gas.
It's not the braking that wastes gas. The problem is that you're using fuel to close the distance between you and a situation where you're going to have to stop. Instead of keeping your foot on the accelerator, let your car coast to that light, applying the brakes later when you need to come to a full stop.
When the light turns green, let up on the brake, but don't hit the gas right away. Instead, let your car get to its coasting speed on its own before hitting the accelerator. It only takes a couple of seconds, and you'll save on fuel.
Some drivers take these fuel-saving driving habits to the extreme, getting as much as 100 miles (160.9 kilometers) per gallon! Check out some of their techniques.