I don't have a specific formula I always use. I tend to switch it up depending on the piece and the vibe. Sometimes I use a lot of different textures and layers to shade, other times I just like pure black and white.
I think you are going in a good direction with this piece! I like the contrast in how detailed the hair on the more flat colors of the skin and shirt.
Thanks so much for the feedback, @terrorfirma! I find myself switching styles or techniques as well. There is so much for me to still learn and explore.