When creating a new illustration where lighting is key, try building a simple 3D model to photograph as a helpful reference. As you'll see in my examples below, it can be a very crude model made with whatever materials you have handy.
I started trying to sketch the figure as a series of basic shapes. Realizing it would be more helpful to see the figure in 3D, I used modeling clay (available in arts and crafts stores), some toothpicks and a pizza box top to recreate the scene in my thumbnail sketch.
Building the scene also gives you the ability to look at angles you may not have considered.
Stay tuned for the final image!