I am not sure if this would really help, but a whole country hand in hand doing the efficiency I believe would help a lot, like not to travel unless it is necessary.
There are lots of things you can do to improve your car's MPG. These include maintenance tips (e.g. keep car tuned, keep air filter clean), general tips (e.g. tire pressure, empty trunk, remove baggage rack etc) and, the most important driving tips (e.g. how to accelerate at what speed to drive, A/C vs open window etc)
You can get a big improvement, up to 25% or even more on you MPG by following them.
There is not enough space here to count them all, so I suggest that pay a visit to [link removed]
It has many more tips depicted, including an explanation on how each certain tip actually helps.
Besides maintenance, the only real safe change you can make to the car is to change the final drive ratio in the differential for less acceleration but more mpg. The job costs a couple hundred bucks though plus maybe another hundred for the new gear if it even exists.
For day to day improvements: Use the gas recommended in the owner's manual, from chevron/texaco/76/shell. The wrong type will hurt. Keep your speed down and ample distance between yourself and the guy in front of you, to minimize pointless braking. Likewise watch the stop lights and cars in front of you so you don't gas & immediately brake for no reason. Note that high acceleration doesn't hurt, only high speed & braking. On the freeway keep a constant throttle or make changes very slowly so that the oxygen sensor can adapt without getting confused, for better mpg.