Some points I could throw up ...
Next time you get your oil changed, have the air filter checked as well. Replacing a dirty air filter with a clean one can save up to 10 percent on fuel costs.
Make sure your vehicle is in top running order. Read your owner's manual and follow the manufacturer's recommended maintenance schedule. If it's time for a tune up, do it and you can realize up to a 4.1 percent increase in fuel economy.
Using the manufacturer's specified motor oil, and changing it per factory recommendations, can improve fuel economy as well, so grease up.
The less weight in your vehicle, the better your fuel economy. Clean out that trunk!
Here is the ultimatum 
Cool down. Fill your tank up on cool mornings. Fuel is denser when cold. Fuel pumps measure by volume, so if you pump when it's cold, you get more gas for your hard earned money.