Act as if there were an egg beneath the gas pedal

A stomp on the gas pedal is just a plain waste. Learn to gradually increase your speed without too much interruption to the flow of traffic. The lighter and more gradually you accelerate, the better efficiency you'll notice. Always think of that egg under your gas pedal. Pick an RPM (1500 - 2000) and always try not to exceed that number.

Drive as if you had no brakes

Personally, one of my favorites. This requires a greater distance between you and the vehicle in front of you. It also requires a heads up for anticipating whats ahead. Maintain a safe distance and speed at all times - just be leary of applying your brakes unneccesarily.

Coast... in Neutral

Manual or automatic transmission, it does not matter. When possible shift your transmission into Neutral and coast. Also, keep and maintain a safe distance between you and the vehicle in front of you - at all times. Without interrupting the flow of traffic (behind you), coasting will yield great results on conserving gas. You may think coasting will only work on downhills - not the case. When applicable, gradually increase your speed in anticipation of a small hill or incline and then shift into Neutral and coast "up" the hill. The rewards here are twofold! Typically, you increase the amount of gas to climb a hill when you are on the hill - think ahead and minimize that effort, and in turn you may use very little (if any) additional gas getting up the hill. And usually, you then are able to continue coasting downhill.

Limit idle time

When getting in your vehicle, buckle up, adjust mirrors, get situated all prior to starting the engine. Make this the last step before you take off. Otherwise, the engine is running and you are sitting idle - diminishing fuel efficiency. In addition to parking facing out, try backing into a parking spot at the highest point of a parking lot - anticipating a roll out before starting the engine. Use caution with allowing your vehicle to move without the engine running! Power brakes and power steering are dependant on your engine running.

Sitting idle in traffic, at a long light, in line at a gas station? Shut the engine off.

Use a gas card and seek out cheapest stations

Find a gas station that historically has the cheapest prices. Sometimes it's a Costco or BJ's Wholesale Club requiring a membership. It still pays to use these stations. For instance, there is a Costco directly across the street from my office. I signed up and applied for an American Express card that also pays 3% back when making gas purchases. That's 12 cents off a gallon at 4 bucks a gallon. So let's say Costco is selling the cheapest gas at $3.87 (where others in the area are hovering around $4.00/gal) and you use your American Express card, you in essence are paying $3.76 a gallon. Combine that with the above gas-saving driving techniques and you'll be getting the biggest bang for your buck, for sure!

Drive safe and sensibly at all times

The techniques listed here will, without a doubt, help improve fuel efficiency. For more "hardcore" tips and techniques, google "hypermiling".