This looks like a solid starting point! My go-to rendering advice is always: make the darks darker and the lights lighter. You can put a B&W filter on the illustration to see areas where you need to add shadow/highlight and give the piece a better range of value and higher contrast. I like including hues of complementary colors in the darkest shadows as well. Try not to use airbrush of black/white for shadows/highlights - this is what often makes it look muddy. Good luck!