If you want to learn how to make "real" people look like those in "classic" portraits, you have already been given some excellent technical advice.

If, on the other hand, your problem is that the young ladies all want to look like the ones on the magazine covers, it might be good to collect a few books by real masters of portraiture--Cunningham and Karsh come to mind--and let your prospective candidates see that a good portrait represents its subject, as opposed to a commercial illustration model. There is a big difference between a subject and a model; essentially, the latter is not "real" except in the image. Keeping Annie Leibovitz' Women around to page through has helped to get this across to a number of people who have since become favorite subjects.