remove excess weight from your car, only fill the tank half way (less weight to pull around all the time), these 2 weight saving measures will help shave off a few pennies at the pump.
check you alignment, ensure your tyres are correctly inflated, make sure your cars oil is of the correct viscosity. these things will help decrease the resistance to your drivetrain abs shoudl also improve eeconomy.
remove any poilers etc you have on the car as they will increase your drag coefficient which has a detrimental effect on your economy.
drive more smoothly, accelerate less quickly, only use enough throttle to get you up to a certain speed and then try to coast as much as you can, worst thing to do for fuel economy is to drive at full throttle and then brake at the last minute,.. better to let your car slow naturally.
some tyre manufacturers have tyres which also help improve economy since they provide less rolling resistance.