The best way to improve gas mileage, on any car or truck, it to keep it well maintained and drive conservatively.
For maintenance, change your filters (air & fuel) at recommended times, check all your fluids (oil, transmission, power steering, etc.) and keep them at the proper level. Again, change them at recommended intervals.
As for driving "conservatively" - I have heard it recommended that if you drive "like there are raw eggs on you gas and brake pedals", you will get better mileage. Accelerate easily and slowly, and plan ahead so that you don't have to use your brakes too hard when you know, in advance, that you will be coming to a stop (like when you see a Red light or stop sign a block or two ahead.
Every time you press the gas, that injects fuel into the system. The more you press the pedal and the longer you keep it pressed, the more gas you will be using.
Doing proper maintenance and then "driving hard" does not save gas.
Take Care, Greg A. (driving for over 30 years)