More pep from a Standard 4-cyl?

Forgive such a beginner question, but I'm curious what can be done to get more pep from a standard 4 cylinder engine (95.5 Isuzu Rodeo)? I'm pretty uneducated in the area and figure the best way to learn is to ask.

http://www.pureisuzu.com/

intake
cam
muffler

are the big ones.