Hm.. I think this picture isn't that bad! It looks quite nice. Just a simple outline of a horse with highlights and shadows. Highlights and shadows are good, and they give the horse a more 3d-feeling. It's really good for a beginning, now you should try to add more details and stuff. Take a reference photo and paint more muscles or something..just mroe detail^^ And if you really want to make this picture wonderfull you should draw the same horse, with more detail, without the lines^^