That's good, you have a good grasp on the concept. You should try adding some shading, but what should help you to improve, is just observe and study as many horse pictures as you can. Observe and understand their muscles and where they are located, and it will help a ton with shading, as well as making it look more realistic... Also, keep drawing and drawing, you will improve everyday.
You say room, I say stall. You say mall, I say barn, you say shopping, I say riding. You say high heels, I say steel-toe boots. You say boys, I say stallions. You say pedicure, I say farrier. Anything you say, I say horses♥