Clockwise = richer. You're turning a screw into a nut attached to the needle, so turning the screw "in" raises the needle for a richer mixture.
Don't forget, that screw is brass (hence relatively soft) and has a limited range. Don't force it. And if you back the screw out of the threads, most likely you'll have to remove the piston to push the needle carrier back in and engage the threads.