One can illuminate a portrait in many ways. There is not only one correct lighting. However, as we study with a live model in my studio, once a week with a number of fellow artists, I prefer a simple set-up: one single light source directly above the head of the model.
1. I use a so-called soft box which I happen to have in my photography equipment. I replace the flash unit that actually belongs to it with an ordinary bright daylight bulb.
2. I hang a sort of curtain between the face and my studio-lights to avoid this light shining on the model's face.
And more in this picture...
3. I made a stand on which the model is posed. In such a way the face is almost the same height as the canvas on my easel. I prefer not to look down on the model. This riser is about 33 cm high. (13 inches)
4. To ensure that the background is not too distracting, I have hung a cloth behind the model.