Untitled

I do enjoy the motion this drawing is attempting to capture! A comment that I would like to provide would be that of the chest, as the straight line could create a bit of a misleading broadness on the chest. One strength that you would be showing would be the conventions of the arms, as they show some of the active pull that could be present on the chain.

This is pretty good! I like what you did with the leg turned to the side, the guidlines show tht you were thinking about its 3d form. I recommend following that for the ribcage and boobs. Combining form with the line of action is pretty tough, but if you keep practicing it then youll make figures that are both dynamic and appear 3d

You have managed to capture a great pose. It's very promising and looks good. I would suggest using more gestural lines; overall, sketchy lines will help your drawing look less flat and naturally add line variations.

Overall good understanding of proportions! Though, the head is a little too small, compared to the rest of the body.
The legs are drawn nicely and you can feel that the left leg is doing a good job holding all the weight of the body.

I think the upper body is the one that needs a little more work. To do that, I recommend studying a little more anatomy: especially the torso, the pelvis and the head. And then, take that information and use it to observe the human body in action.
Anatomy will tell you how the pectoralis major connects to the humerus, how the deltoids connect to the clavicles and the scapulae, and so on. And how does that affect the body when doing a pose such as this one?
By knowing what muscles and bones are making up the torso and the rest of the body, you can slowly try to break down every pose and better understand why such shapes are there. And with that, drawing will be a little more easy. 
Anyway, you are doing an amazing job, keep going! ^^

You can add contour lines on the limbs to suggest perspective. For the thoracic area, you can use lines to hint at the underlying structure, especially the downward-slanting ribs. It’s recommended to draw some of the bony landmarks that can be observed with the naked eye.