Anthony, I usually paint the faces burnt sienna first, then blend a mixture of yellow ochre & white in, taking care to leave the recesses dark. This gives my basic shadow. I then highlight the obvious areas like the forehead, nose and cheekbones. When totally dry, I drybrush a small amount of flesh overall. I then reline the eyelids and add the pupils. You are not supposed to see the white of the eyes. Invest in a 0/10 & 0/5 brush for the fine lines and a #1 brush for the large areas.
Clothing:- I paint an overall darker base colour for the uniform, making the creases/shadows prominent. The plain base clour is the drybrushed on and a lighter shade drybrushed on for highlights. A thin wash is applied afterwards to further accentuate the shadows.
Keep practicing and happy modelling.
Tappie.