In our high-tech world, we have a huge thirst for convenience (or at least, things that are supposed to be convenient). This can mean that the first thing we look for is a gadget to do whatever we want to do for us.
It can be the same with cars. People fall for scammers who sell "miracle" devices to improve gas mileage (Consumer Reports tested many of those, and found that they don't work), or they look for genuinely useful gadgets like MPG meters, or they spent a bit more money to buy a fuel-efficient hybrid car.
That can make a difference, sometimes significant. But the very first thing that everybody should do also happen to be the most inexpensive: Learn to use the gas pedal properly. This might seem obvious, but we tend to forget that once we've bought a car, this is the single biggest factor in determining gas mileage.
You won't get Prius—like MPG in a Ford F-150, but the variability in MPG for a single car model can be very high. Just learning to drive, as much as possible, at a constant speed can make a huge different since coasting burns less fuel—everything else being equal—than acceleration (and unneeded deceleration also leads to poorer gas mileage, since it just leads to more acceleration on average to compensate).
This post might not be a "ah-ha!" type of article that tells you something you didn't already know about, but often the most important things are also the most obvious; so obvious that we get bored with them and forget about them.
So stop thinking about fancy gadgets or hybrid cars. These things can be good, but only after you've started with the basics, so learn to focus on making a difference with your gas pedal.