Working From Large To Small

When I draw the figure from life I generally work from large shapes to smaller shapes. I might start with a gestural block-in for placement and proceed to loosely and lightly lay-in tone to indicate the largest masses. I don't spend too much time on the outer edge of the form because I know the pose will change a bit from one sitting to the next and even the best models move a bit during the pose. I tend to resolve an area in a form of drawing shorthand that allows me to recall the pose and the lighting even without the model there.
Beginning with the pattern of light and shadow is the key. I often see students making an infinite number of measurements and missing a sense of the whole form and underlying structure. There is also a tendency to place hash marks for the eyes, nose, crease of the lips, ears etc. at predetermined generalized distances, I call it the football head approach because at some point the drawing looks like a football. The oval shape, the center line and hash marks. I'm not a fan of the football life drawing game, it prevents real observation.
When you work your way to placement of the features, see the structure and simplify it. Think sculpturally about form.