Well surface details can be in different forms, but in your case its mostly scales and lizard skin. i recommend following Dan Katcher’s workflow from one of Zbrush summits. it was something similar to this:
use scale alphas in combination with spotlight, stretch the alpha on the skin and after you are finished just drag the scales out using a move or the displacement brush.
and if i want to just give some hints, remember that scales are most beautiful when they follow a flow and have a pattern. they have direction and grow and shrink in size as you follow that direction. try to look at real life lizards to get some idea of how it should look like. now Dan’s workflow allows for this, but it might be a bit time consuming.
u can also use contrast in deformation menu in combination with morph targets to amplify the details further.
i hope this helps!