not drive?
well you could start buy making sure you've done all your maintenance/tune up stuff. Change all the oils, preferably to synthetic, replace your air filter with a high quality one (k and n for example), change your spark plugs, and don't have anything that isn't neccessary inside your truck, the weight actually made a difference for me. If your a 5 speed, shift at 2500 rpm and don't book it all the time. Also make sure your tires are inflated properly and bearings are in good shape. All this stuff, including fuel filter change as well, brought my truck up from 16mpg to 20mpg
hope that helps