Saving energy > Cars

Don't over-load a car. The heavier a car is loaded the more gasoline it requires.
Use air conditioning only when necessary.
Aggressive driving (speeding, rapid acceleration, and braking hard) wastes gasoline.
When buying a new car, compare the fuel efficiency of different models and let this knowledge guide you in your decision on which car to buy.
Combine trips: short trips, each one taken from a cold start, can use twice as much fuel as one trip covering the same distance when the engine is warm.
Using cruise control on the highway helps you maintain a constant speed and, often, save gasoline.
Tires need to be properly inflated.
Make sure the car has clean air and oil filters. Don't miss your car's check-ups.