I was teaching live drawing in a community college and students started zoning in on the face and spending a couple of hours on that and then putting the rest of the body on the face only in the last hour. It didn't work to just tell them, 'Well, you're really not thinking of the body as a totality.' So in desperation I would put a drape over the model's head so they couldn't see it. They had to draw the body and then at the end of the session for an hour I would take the drape off just to try to reverse their procedure.