Start with the obvious.
Give it a good tune up. New wires, plugs, rotor, oil flush, tranny flush, coolant flush, fuel filter, fuel system cleaner/treatment, full tank of premium gas, etc.
A free flowing air filter will free up some lost power. I like K&N and Holley.
Exhaust is a plus. Headers, dual 2.5" H-Pipe would work very well.
If you want to dive even more deeply into it, have your heads machined. Full valve job, gasket match job on the ports, some good valves and valve springs, and maybe even some roller tip rocker arms to get rid of some friction.
All will add power, most arent time consuming at all. Depends on how much you want to spend, and how much power you want. That head job will cost close to a grand at a good machine shop, while the tune up, filter, and exhaust may cost half that depending on brands, sales, and doing the work yourself.