I know this is old an old thread but maybe I can contribute. I used to drive a car with an instant mpg gauge that would factor in miles per hour and not just the type that goes strictly off of vacuum. You learn a lot with a gauge like that. Obviously don't drive like you're trying to win a race or something but there's way more to it. When taking off from a stop, if you get on it hard you're wasting fuel but at the same time accelerating too slow will too. Your best mpg will be once you are at your desired speed. Another tip, although not for everyone and may be a safety concern for some and I'm just passing info not recommending, coasting in neautral when possible. There's times I can coast for over a mile and still maintain the speed limit. There is a bit of science to it though. Never get the car below your desired speed or you'll have to accelerate to get there and that'll use more gas. And if the hill is just steep enough to coast a second or two don't bother especially with an auto. From driving like a normal descent driver to taking extreme measures in driving habits I've gotten a car from 20 improved to 24 mpg. Another tip for auto cars is shut it off before you put it in park. Make sure your foot is on the brake! You're only saving a second or two of run time, but without a doubt it will save you some gas.
There is no magic to getting good fuel mileage. The biggest factor is what the vehicle is and driving style.