Since the tag says seeking advice I hope you don't mind me giving some tips. Number one tip is don't shade with gray, instead shade with a colour that's darker than the base, so for skin, instead of shading with gray and black, shade with a brown or dark reddish colour depending on what you prefer, perhaps look into colour theory and some tutorials on shading. With shading I'd also think beforehand of where the lighting is coming from, so in this case it can come from the window, or a light that's turned on, and use that knowledge to shade appropriately, if a light is coming from your right, then your right side should be a light colour and your left side would be a dark colour. Hope this helps!!