Attached Link: http://arcana.daz3d.com/tutorial.php?id=2

Anton has a tutorial for adding skin texture (pores, lines, wrinkles, etc) without compomising the color of the skin - read it here: http://arcana.daz3d.com/tutorial.php?id=2

To make the greyscale (see tutorial) layers i usually use add noise, or texturize layer using a bumpy surface, such as canvas or sandtone

Good luck!