As well as working with live nature it is also a good idea to sketch bones/ skeletons to give understand how bone anatomy works and also to be inspired from it, so that the artist can apply this to their concept art.

working with natural form the artist, Feng Zhu also speaks about how it is important to learn how to sketch buildings, however starting from something simple, like huts. This would teach you perspective, so would natural form drawings, but help you to work with size and proportion when it comes to drawing a full scene. That’s if you are going to do that. If you just want to concentrate on character design then you can, however this will help you with above skills as mentioned.