I fail compared to most people posting in here, but meh! But WTF is going on with that left arm, I just can't get it to look right...
I find it really helpful to draw lines to represent the skeleton and then draw over it. That way you know your proportions are correct and it's much easier to imagine how the body is bending. The problem with the arm is the elbow. It's a bit too rounded and there's nowhere for the bone to realistically exist without bending.
Hope that's helpful!