There is very little you can do in the way of modification to improve the mileage on that vehicle. The best things you can do are to make sure the tires are inflated to the maximum recommended pressure, change the fuel filter regularly, and keep it tuned up sharply. It also could be worthwhile to use a higher output coil (if you have
the 4 tower coil) or coils (if you have the coil on plug system).
Places like Summit Racing have Accel and MSD performance coils which
are made for your engine. Then you may gain by some experimenting with different brands and types of spark plugs (but NOT those $25 ea plugs which claim to have a capacitor in them). NGK G-power platinum, Autolite XP series, Champion Iridium, Bosch platinum +2, or Brisk LGS or silver racing (in the recommended heat range) might improve things.
If your vehicle does not have a mileage computer, it would also be worthwhile to install a vacuum gauge near the dashboard, so you can get feedback on the effect of engine adjustments, and the effect of your driving style on economy.
There is also an exhaust system manufacturer in Southern California named Gibson; who builds exhaust headers, mufflers, and complete systems which can improve fuel economy. Gibson is the ONLY manufacturer I'd recommmend for this purpose.
But many of these things cost a substantial amount of money; and the results are largely experimental. If you really want to save fuel; the surest way to do that would be to get a bicycle or motorcycle.