Right now, your light sources are all over the place. You would be better served by picking just one direction for your light and sticking with it throughout the piece. Multiple sources are way too difficult for beginners.
Try drawing from observation, rather than trying to invent your own lighting. If you have no access to a live model, set up a doll or copy of classical greek statuary (the more anatomically correct, the better) with a single light source and observe how the light plays off of the rounded forms of the body.
Also, to simulate the effect of metallic skin, set up and draw some shiny metallic objects for practice. And look into the work of Julie Bell. That's one of her main painting themes.
As the ego shrinks, so the spirit expands.