A good piece! The more you experiment, the more you will learn.
A tip for shading: Imagine a light shining from one angle, the way it shines against an object, and how the shadow would bend around the other side. It will all come down to how well you know light contours the shapes you have in mind as well as the shadows it makes. Perhaps take pictures, be they from your own merit or maybe photographs online, and attempt to mimic what you see. Start with geometric shapes like cubes or spheres and move to cloth folds and the like.