My Prius has a display which shows MPG either instantaneously or cumulatively for a given trip. The effect of changes in driving habits provides immediate feedback. I am astounded at how it has changed my driving, even without an active effort on my part. I now routinely get 55-60 MPG on my daily commute, 27 miles round trip.
What has changed the most is that I keep a greater distance between me and the car in front. Their brake lights are on and off all the time, mine almost never as I simply let up then gently accelerate, closing and opening the distance as needed. I also tend to drive more slowly, yet arrive in the same amount of time (it all evens out in the last stretch of road with about 3 miles of frequent traffic lights). Another big change is that I accelerate pretty moderately, a big gas saver.
OK, I admit that until I sold my BMW K1200LT motorcycle a few months ago I did get some kicks from uhh.. well.. let's just say spirited riding, but now it's just me and the Prius.