Keep it simple, and you'll save!

* Make sure you remember to put your gas cap back on securely after filling up.
* Take the highway to avoid stop-and-go traffic in the city if you can, but don't drive over 65 mph! Anything over that will eat up gas faster.
* Don't let your engine idle for very long, if it's going to be more than about a minute or so - turn the car off.
* Don't run the A/C if you don't really need it. Use your windows, the vent, etc.
* No matter how frustrated you get, avoid gunning the engine when ticked off at bad drivers.
* Park ‘n Ride. If you live in a city that has public transportation you can park your car at the nearest stop on the bus line and then ride the bus the rest of the way to and from work, for a fraction of what it might cost to fill your tank up every week.