The main trick is learning to coordinate your foot with what your hands are doing. Just play around with it for a bit. Try doing slow wah sweeps while playing a riff or passage. Try sweeping it up and down in a pattern while playing. Try sweeping on individual sustained notes. Try setting or holding the wah at a "fixed position" (i.e., all the way up, or halfway down, etc.) and play while in that position. Throw some distortion before the wah for some crazy screaming solos, or toss it behind the wah for something more subtle, but still cool. Or my favorite: place a delay pedal after your wah and try sweeping while playing. It gets freaky.
Experiment with these kinds of possibilities, and you'll get an idea of what you can do with a wah pedal.
