I used to find the thought of painting faces intimidating and overwhelming, but once it really clicked that faces are just like anything else - a mix of shadows, mid-tones, and highlights it was like my (painting) world opened up.

 

I use this approach in my more elaborate paintings too. Here's the reference image I used, and the painting I made from it below:

If you look at the painted face, you can see I used 3 main shades: the highlight, mid-tone, and shadow, with a little pink for the lips, and some others colours for the eyes. It's the same principle, expanded slightly.

I really love painting faces, and I hope I can share some of that joy with you.