Quoted By:
Work on your grasp of proportions first. For instance, the torso for the top left figure is way too long, and the legs are way too short. The hands are too small. The neck is a complete disaster, and the heads you're drawing are too small, flat, and skinny.
It might help if you started drawing actual human beings. You won't get anywhere with human anatomy if you don't know what a real body looks like.