What's on display : buttocks
Why it works : The voyeuristic audience has been caught in the act! In this electrifying moment of discovery, the subject seems to affirm with her expression "Yes, I see you checking me out. No, I don't particularly mind." Or, alternately, "What the -- HEY!" Either has a distinct attitude.
What's important : We see many parts of the body in dynamic opposition to each other. The torso twists in conjunction with the neck. There are creases at the trapezius and the back. Eyes are looking at the viewer, whatever it is (sometimes us), in a flirtatious or startled manner. The shoulder nearest the chin presents a good opportunity for overlap. The breast is often seen in profile or semi-profile.
Hair for cover : Don't like drawing necks or backs? Let her hair down! Hair tends to whoosh around slightly when the head turns, so this can be exaggerated and otherwise exploited to the lazy artist's advantage.