Important areas for shading are the eye sockets, the temples, the side of the nose and below the cheekbones. You draw the lines with a flat sable-hair brush. By placing it obliquely on the skin you get a sharp edge on one side and a fading effect on the other side. To determine which side should be sharp and which side faded, you start from the centre of the face (nose). Create a fading effect towards the outside.
The parts of the face that have not been shaded now seem to have been brought forward.