TRSE: How To Draw Tutorials:
The Basics of 3D Drawing

    Whenever a character expands a hand toward someone (or camera), the spread hand will seem as big as the head itself as shown in the sketch above. If you have a big mirror nearby, give that pose a try in the front of the mirror, and you can change the pose of your hands (fist, pointing, V-sign, whatever). Compare your hand with your head as you change the distance between your hand and your head.
        When a head is kept straight up, the "halo" of light reflected off hair will seem to be straight across the smooth hair, but when the head is shifted to a different position without changing the point of view. the halo would change its shape in respect to the fact that the top of head is somewhat domed (top of ball). The reflections and shapes can make 3D far more complicated but don't worry about that for now.
    This is a simple sketch of Shuang (my own character) chasing her feathered dragon pet who stole her bandanna. Since her body tend to lean forward while running (try it yourself) with her hands expanded in her futile attempt to catch her pet, she would have to look somewhat 3D. What can be done is just add the arcs (crescents) to her body to outline her clothing or belts to make her look bit more 3D. One of her legs looks bigger than the other leg because of the fact that her legs are swinging while running. Notice how the background shrinks toward the focus point and even the bandanna trailing from the jaws of the dino/dragon pet is pointing toward the focus point because that animal is running quite fast.