I suggest that beginners don't need to spend too much time practicing this kind of skeleton structure. I don't think drawing such detailed skeletons is actually that helpful for beginners' learning and understanding.
You could try adding muscles and clothing to these figure skeletons you've drawn. You might find that eventually you'll just abandon trying to make the muscles and clothing conform to the skeleton, and instead draw entirely based on your intuition. That's when you'll understand why I say not to spend too much time practicing this type of skeleton at the beginning.
I don't mean you should start drawing characters out of thin air—rather, practice using simpler and faster methods. I agree with @NickRowler 's suggestion of "practicing gesture drawings with a focus on form."
