Here's a couple of ideas on how to save a little money on gas:
Edmunds.com, the car site, tested various theories a few years ago on how to improve your car's gas mileage. Their findings are here. The executive summary: Driving slower works, using cruise control works, driving in an easygoing manner is useful and idling for long periods of time is a bad idea. It doesn't matter much whether you turn on your air conditioning or have your tires filled with just the right amount of air.