There are many ways to depict the figure and I'm not pretending that this is,"the way" to do so but it has helped me in my work very much so far. I always measure the figure in heads. When I measure the head, I use the neck as well. This technique was handed down to me by th great June Brigman. She was my figure drawing teacher at Kubert School and the creator of Marvel's Power Pack http://en.wikipedia.org/wiki/Power_Pack
The reason I love to include the neck(or what is viewable of the neck depending on the pose and angle) is because the portrait is from the crown of the head to the clavicle. Think about it, you really only see just the face with no neck in a wanted poster or criminal investigaton sketch. A beautiful woman like Andrea Rosu is going to have a far differently structured neck than a body builder like myself. Where as hers is more graceful, mine is very utilitarian.
The chin to clavicle ratio is very important as well. Once I've established this mass, I usually use it to measure out the rest of the figure. This has served me well on a sketch pad, large paintings, and also murals. Below are some works by Scott at the Art Students League that I modeled for and some pieces I drew of ftiness model Andrea Rosu. I hope this was helpful.