Rough in the large shapes, think light shape / dark shape, those are your choices. Feel free to manipulate the subject to serve your design. I don't want to get stuck anywhere too long, that is especially true of the face, a place that's very easy to get hung up on.
Start breaking the big shapes into smaller ones, which is the beginning of describing "things". Surprising how little needs to be done, try not to go too far. Keep asking yourself, "have I fractured a big shape by putting too many values inside of it?"
I decided to add Terra Rosa and Yellow Ochre to the palette which is much easier now that I have the values established.