For Best fuel savings is drive less. (group errands, carpool, and do the farthest spot first then work way back home). Leave early for errands so you're not rushed and tempted to drive more aggressively.
Remove extra weight from your car (clean out your trunk). Inflate tires to proper rating to reduce rolling resistance. Maintain vehicle tune ups, wheel alignment, bearings, brakes ect. Avoid using the heater use until the engine has reached operating temperature. Minimize air conditioning use, below 40mph use windows, park in shade use sun shield when parked. dress for the weather. When driving on a multi-lane roadway, try to maintain a "space cushion" around you, so you can avoid speed variations. Conserve momentum avoid coming to a complete stop whenever possible. Be aware of your surroundings, try not to drive in a manner that will annoy those around you, give the impatient drivers an easy opportunity to pass you. Some will see your atypical driving style and give you a thumbs up, most will be annoyed that you held them up from a very important stop light they rushed up to, only to wait until it changes green, right about the time you gently roll up to the light.