Step 4: Painting
You need special paints or at least a latex base to mix with your paints for latex masks. Again, Monster Makers has a great selection of supplies to get you going.
I had a hard time getting a nice balance between a warm flesh tone, and an old wizard pallor. You can see I started with a slick coating of flesh tone, and painted in some dark shadows. Next I added veins and liver spots to really add some aging. I didn't get too detailed, but tried to hit it just enough for some realism.