I'm a touch confused with what your asking, do you mean detials in maya form Z or actually making them in Z?

If its the first, look into displacement maps (lots of help on You tube and Zbrush Central), if its the latter, your going to have to up the poly count in Z to add details, about 1 million should be enough, but you might need to go higher, Z3 handels this pretty well. If not just mask off areas and add detial to that are and move on.

If your not sure about adding detials at this level, you need alphas (for pores, scales etc) theres quite a few available free on the internet (highend3d and Antropus Costa's site)

Hope it helps