Two words:
Liquid. Latex.
Buy it at most art supply stores, and some costume stores.
Brush it on, apply bits of toilet paper over top, brush again over the toilet paper, rip. Add in bits of oatmeal for effect.
Do your whole face with just regular white cream makeup, be careful not to use too much. Then go in under your eyes with black and blue. Go over your oatmealy bits with a variety of colours from one of those cheap makeup kits, no need to be too careful. Add blood.
I've also read that you can use white school glue rather than liquid latex for applying the toilet paper and oatmeal. Haven't tried that, I imagine it would work but that it would dry harder and much less flexible so it would probably need to be done more sparingly. It would definitely be cheaper though.