Our model today was Diana Carey. As a short demo today I made a drawing and just blocked in the large highlight and shadow. I worked on the drawing a little more after the demo but what is important here is, once again, over-all highlights and shadows need to happen before "local" highlights and shadows. After the demo I went in to the over-all shadow and added some more "local" or specific highlights and shadows but I was careful to not allow these highlights in the shadow area to get as light as the highlights in the over-all highlight area. Doing so would contradict the light logic I set up when I blocked things in.
Another point worth emphasizing is that it is important to guard your lightest highlights. There are usually very few places on the figure that will be the lightest light.
I also mentioned to several of you today that it is difficult to achieve a wide range of values with vine charcoal. It is too delicate. Smudging it at all will remove most of the charcoal. Vine is good for the beginning of a drawing when you want to be able to remove lines without leaving much of a mark. If you want really dark values and if you want a wide range of values, I would suggest that you finish your drawing with compressed charcoal.