Hello and welcome to EM!
The first thing you can do is
slow down. Wind resistance at highway speeds is a mpg killer. Usually a 5 mph reduction will get you around 8% increase in mileage. Combine that with other driving techniques will net you a lot more.
Look at this page for more driving tips. You should also look into purchasing a scangauge as that will greatly help you fine tune your driving style. The next thing I'd look into would be aerodynamic mods, but driving techniques will be the #1 fuel saver.