As the old story goes, the visitor to New York asks the local, "how do I get to Carnegie Hall?" He is told, "Practice, practice, practice."
Do you know any figure painters near you who could mentor you in the practice of painting faces? This would be the quickest route to inmprovement.
What I do is put a base coat of burnt sienna and white, roughly matching my own skin color. When this has dried, I apply a coat of thinned burnt sienna so most of the color stays in the folds and creases and only tints the forhead and cheeks. After this has dried, I mix burnt sienna and white again and just hit the highlights in progessively lighter shades. In 1/35-54mm, lips should be very subtle, maybe just the slightest addition of red or Alizarin Crimson to the highlight color. Depending on the scuplting, eyes may just be a tiny drop of thinned Van Dyke Brown, so it flows and leaves a squinty look, or if the socket is very defined, you could add the lightest shade of highlight color, but not pure white, then a tiny, tiny, spot of dark color (black, van dyke brown, Prussian blue, etc) for the pupil/iris. You may need to go back with various levels of highlight , base or shadow to further define this.
Of all the challenges of figure painting, getting the face right is probably the greatest.