Hey these are great!! Just keep drawing first of all, and you shouldn't have an problems developing. Draw from magazines, internet, t.v. There's an oceon of reference for life drawing or anything else at that matter. Just draw what you see. Exercise your eyesight, thats the key. I'm not sure about boxes and cylinders, it might work, but that type of process always complicated me, I mean if you have a model, try to draw the model as you are seeing it. Yeah start out with basic shapes, but honestly,its hard enough without having to invent objects that are'nt there, you are already going to be battling against a symbol system, thats going to be trying its best to get in the way of reality. I would probably go with countour too, looking at your model more than your paper, drawing quick and lightly. These look fantastic, keep drawing everyday, find reference everywhere, sports pages, the library, and you'll definately grow.