You're in the "brush" phase. Everything you do is determined on your brushes, and you don't seem to be resizing them a lot. You're experimenting as you do on with them though i can see. Multiple colors overlapping for a popout effect. But Black doesn't have a white shadow.
Try and think of what you plan to do in the piece, work from there and try and keep a focal and a good flow of direction. Practice will make perfect and I recommend you try looking up tutorials on Deviantart.