Thanks for stopping by my sketchbook. Couple of things. The Barque needs to be brought up as one. You have laid it in but the shading in the shoulder is getting way ahead of yourself. Draw the shape of each shadow and fill it very lightly. Correct as necessary. Also, if this is your first one go easy on yourself and do a simpler drawing, I sure as hell did. That ones a complicated one to say the least. I admire your enthusiasm though.
I bought a book called 'Anatomy Lessons from the masters' and copied a mess of drawings out of it. Did wonders for my drawing technique, I highly suggest you take a peek.
Best of luck.