Agree with Read that you seem to have you proportions pretty well figured out. Shading and using cross contour lines to give shape will help a lot. Most of your shading is straight and vertical. If instead you make marks that followed the shape of the body part it would give it more of a full 3D look. Using the second drawing, the guy with the cape and sort of a Galactus helmet. If instead of coloring up and down in straight lines you make the marks horizontal and followed the curve at the bottom of the cape, it would give the cape a much more filled out look like it is curving away from your eye. I hope that makes sense.

Hi. Nice job. One can see that you are understanding and naturally intuiting some very important ideas. Your proportions are good and there are places were the drawings are developing some solid form. In other places though you are losing the form or making a mark that flattens it and therefore the drawing lives in two worlds, the 3 dimensional, and the 2 dimensional of the paper plane. You want to try to find and refine these areas. Take your time. Make the lines that you put on the page more refined and more purposeful as the drawing develops. Additionally, i would say that as you add value and shading remember to think about light and form. In the beginning imagine there is only one light source falling on all the forms and be very specific about how that light is behaving because the way the light falls on a form, in combination with the terminator edge of the shadow shape, will help describe what that form is doing in space. In some of your drawings right now it seems like the shadow is placed a bit arbitrary but remember that shadows are extremely specific to the forms that they fall on and are cast by, therefore they are one of the key ways to describe and build dimensionality in a drawing. Hope this is helpful. Keep up the great work. More drawings mean you are getting closer to being able to speak with your artwork. That is a great gift to have.