Here are several poses that show distinct shadow patterns. We'll have similar lighting conditions on Wednesday, so it would be good to practice seeing the shadows as a separate layer from the initial local color wash and strokes.
Try painting just the shadow shape a few times. This will help you look through the array of layers and focus on one at a time. It will also reveal the role of the shadow shapes. Do the first few in monochrome, so you aren't distracted by color.
You might also try painting the first layer of the figure twice and adding the shadows to just one of those. This will make very clear how much of the illusion of light and 3-dimensionality comes from the shadows.
After you gain some confidence, try painting a few shadow patterns without drawing them first. Stay relaxed, and allow yourself the luxury of inaccuracy. See if your mistakes reveal where you really need to be careful and where some leeway exists.
Have fun, and don't forget to bring plenty of paper to our next session.