I split this post into its own topic, since while it's related to figure drawing, it is also its own contained question, and I thought others might benefit from the answers being easily findable.
There are a lot of different methods of doing face gestures, but this is how I do it:
At 30 seconds, I try for a shape to represent the head. That might be an oval, a rectangle, whatever I see most strongly in the person's features. Sometimes, it turns out to be two shapes, because from the side I need to represent the bulge of the back of the skull where the brain pan hangs out. Then, I draw the "crosshairs" that represent the midlines of the face, along which the nose and eyes will rest. These are just two lines that I will use as a guide, not any actual features.
At 60 seconds, I do the above, but rough in the shape of the eyes and maybe a line to represent the mouth. Maybe I also draw a line to represent where the bottom of the nose will fall.
At 120 seconds, I do the above, then go back and make corrections to try and get the proportions more dialed in. I might erase some of the outlines of my face circle and redraw to account for the "dip" of the eye socket, or the jut of the cheekbone.
With enough time to finish refining the comparisons and proportions, I might then attempt to draw the features on to my now measured face frame.