Hi, i highly recomend a book tittled "Constructive Anatomy" by George B. Bridgman, the explanations are a little bit tough to understand but the examples in this book really helped me to understand anatomy in a more dynamic way, for your drawings, I personally think it's better if you start your skeleton with 2 boxes and a line that represents the spine and simple lines to indicate the arms and legs, after it you can draw over these boxes and start making the shapes of the body.