There are only a few different poses people assume when they wait in waiting rooms. However, I never tire of figuring out the relationship between the angle of the head axis and the shoulder plane; the length of the upper arm compared with the lower arm; the relative position of the legs, et cetera.  The act of sketching makes one observe people more keenly.

Woman with Heavy Arm
Pencil Sketch
5.5″x8.5″ 138# Cold Pressed Mix Media Paper