One of the best ways to improve your car's fuel efficiency is to anticipate when you will need to stop. After looking ahead and seeing where traffic has stopped, coasting and safely braking can really save gas. Aggressive drivers who brake suddenly can actually burn 20% more fuel. Another tip is to use your air conditioner sparingly. On nice days, when you're driving at low speeds, open the windows or open the vents. You should use the air conditioner only as needed when driving on highways. Opening windows at high speeds creates drag, which decreases fuel efficiency.