This is an extremely simple method of photomanipulating a texture onto someone's face. There is TONS of room to experiment in this tutorial so don't be afraid to try new textures and techniques. Don't forget that this is a SIMPLE method to texturising, there are more involved methods to enhance your effects, but this should give you a fairly good guideline to experiment around.
I hope you find this useful.
Step one - find a stock. Choose your stock carefully, to texture properly you'll need a good percentage of skin area to work with, the more the better in my opinion.
Step two - this is simple. Duplicate your stock and set to multiply. This darkens the image on a whole. Then entirely desaturate your multiply layer using ctrl+u and saturating to -100. This will make texturising a lot easier, and creates a better atmosphere for the dark style of manipulation.
Next, grab your texture.
Step three - Texturising. This is the final part, how you go about it determines the outcome, i'm using just one texture here, don't be afraid to use many different types to achieve the desired effect. Add your texture as a new layer, and desaturate to -50 by using ctrl+u, thus making blending smoother. Now set the blending mode to hard light. This should make it blend fairly well, some textures blend better than others of course.
Don't forget, you can rotate, flip, distort textures to make the effect different. This is where you EXPERIMENT. Now just erase parts with a soft brush that you don't want, like overlapping textures etc. Another good idea to strengthen textures is to duplicate the layer and merge down with the original, thus strengthening the texture effect. How you take it is up to you.
Another tip is for holes, with a texture with a hole, if it's not dark enough, use the burn tool on the texture to make it seem deeper.