This is the way I have had most success in painting faces

1. Paint in the white of the eyes. Matt White
2. Paint in the pupils by using a stripe rather than a dot. Black Grey
3. Paint in the base flesh tone shaping the eyes. Bugman's Glow
4. Paint in the lighter flesh tone. Try to leave a small edge of the darker flesh tone as this gives instant shading. Also double or triple coat the raised areas to give a subtle highlight. Kislev Flesh
5. For stubble add a little grey to some flesh tone and paint on a beard pattern. Ash Grey