This tutorial by Derrick Sesson shows us how to create a realistic skin texture. He uses Photoshop and Maya, but the techniques are pretty app independent, so enjoy!
Derrick Sesson writes:
I've made a tutorial on the process of creating semi-realistic textures from scratch in Photoshop for the use of a 3d render of a character.
I show the process of building each layer up from simple images found online, and quickly adding form and texture to our skin with very little effort.