Dissecting Objects

We were taught about reducing a surface of an object and how to sketch them out on perspective. I did some sketches on that...

I found this project not quite hard as I am quite comfortable with forms after a lot of practice. Some of the shapes are meant to be uneven, like how I wanted and some are even. The only part I don’t seem to get is the shadings that is suppose to make the object looks more 3 dimensional. I have quite a difficult time doing that.