Select which colours to use by sampling right out of the picture. Double-click the Eyedropper tool and change the Raster Sample Size at the bottom to 5 points to get a broad metering of colour. If you want a brighter colour for the foreground figures or a more specific colour selection, switch the Raster Sample Size back to 1 point.
Now you’re ready to begin painting in the colour. Beginning with the ‘Hair’ on a new sub-layer, define the larger chunks or shapes of solid colour, starting with darkest shadows. Focus on making shapes that are descriptive and in tone with the others.
Limit the palette to a few shades and place each new successive colour behind the other. You can move a shape behind another on the same layer or sub-layer by pressing Apple-Shift-[ or by going to Object>Arrange>SendToBack.
Use a new sub-layer for each facial feature. Zoom in while you’re drawing detailed areas such as the eyes and nose, and add more detail with smaller shapes to emphasize those areas. On the sub-layer called Face, begin to describe as accurately as possible the general planes of the face.
Continue to define the planes of the neck and shirt on a new sub-layer. Avoid using too many little shapes or it will draw attention away from the figure’s face.