Great shading on those bones! I say, keep on pushing and drawing everything and everybody (Damn there's not much to say abuot what you should do, since you're SO on the right track right no!)
Whatever, when drawing, do some more measuring, pinpoint proportions. Use tools if you must, but remember that the most important tool is your guts. If something doesn't feel right, think and think and think and revise until it gets better. It's really about your own observation. The measring exercises help you seeing more things. And the construction exercises help you to feel your drawings.