I've found something that has helped me to drive slower and be more conscious of my mileage. My vehicle is equipped with a trip computer (or whatever it's called). It can display things like; fuel used, range, average speed, average mileage and real time mileage. I can see how bad the mileage gets when I step hard on the pedal. When I'm on the highway, I watch the mileage just as much as the speedometer.
If more cars had these...more people would be aware of how their driving habits affect their mileage. Of course buying a more economical vehicle would help even more.