Hey, if you're going to practice shading, don't EVER use the airbrush. The colours are cute and you seem to have no problem with colour leaking, but the airbrush should be reserved for highlights and small metallic details, or for blocking out colours if you like doing that. If y0ou like a painterly style, try using the water brush or the normal paint brush. I use the pen + water, but my art is a bit more cell shading-y so that's more personal.