What are some simple guidelines that will help you stay on track with a quick sketch portrait? Stuart Loughridge offers some demonstrations for approaching a portrait by understanding the underlying structure: the overall tilt of the head, where the features sit, and how everything works together.
For quick sittings it helps to get a similar likeness of the sitter. But for a portrait commission where the likeness needs to be perfect, it would need to take more time. Start by laying in the oval of the head, then you can judge its placement on the paper. Draw the oval to the tilt of the sitter’s head. You might look for the shoulders. Now you can sketch in the placement of the brow line and the turn of the head.
Experiment with drawing the turn of the head in space with either an oval or a cube. Now you can place the nose and mouth. Lay it in and correct as you go instead of looking for perfection at the beginning. Look for the triangle of the outside of the brows to the bottom of the lower lip. Then you can think about symmetrical structures. The bridge of the nose may be next to incorporate. Look for the light and the shadows on the structures on both sides to keep things symmetrical.
Start out with a circle for the eyes and nose and build off of it. Even if you can’t see a line you should be able to see that it’s there structurally. You don’t need to be concerned about getting an exact likeness, but getting the structure in will allow you to impose the sitter’s unique face. So understanding the structure will help you get rolling so that eventually you’ll be able to get a one hour finished portrait.