I'm probably not the best person to ask, I rarely draw, and even less digital. But when I did once draw a person, I used the same method I like using when painting traditionally, which basically means I layer on skintones in darker and lighter shades, sometimes mixing a bit of gray or white into specific tones, but otherwise using the same tone. And then I pile it up and smudge it.
I once posted what happened when I only activated the facial layers of said drawing, basically only the layers that came with the eyes, mouth, nose, and lips.
But then again, I'm pretty sure I'm not doing what other people are doing, so I don't know if my type of drawing should be taken as advice.