Drive like a grandma!
Check tire pressure to make sure that it is within normal limits...this is probably the best thing to do. Higher tire pressure = better fuel economy. However, on my car, it doesn't make much difference...so, i stay at recommended psi. Avoid under-inflation!
Don't drive with the windows open.
You can also take off any fender flares or running boards because these things are not aerodynamic.
Minimize blasting your A/C.
Keep electronics usage to moderation.
Avoid fast acceleration. Avoid going over speed limit. Basically, the faster you go, the more gas you use, especially in a tank like ours.
Avoid bling-bling huge rims...more weight to your car.
Avoid putting on off-road or all-terrain LT tires...more weight to your car. Those Dunlops or highway tires have the advantage here.
Avoid excessive unnecessary cargo weight (including mother-in law).
Drive only with the wind behind your back. Stay at home if you're heading into the wind. Good reason to tell your boss.

Although this may be an impractical suggestion, it makes a HUGE difference, especially in big SUVs. Or, more practical, drive slower when heading against the wind.
What i am doing is getting an econobox (maybe chevy cobalt). It actually does not make much financial sense because i would have to own the econobox 10-15 years before i see any financial return on it, but it will also save miles on my car.
Gas prices are killer these days. I have to fill premium gas every 5-6 days! And this is mostly highway driving!!

Damn fat ass (the car, not me) and brickwall aerodynamics!