Stille Nacht
Stand in the middle of a (cold) room, naked (this is optional). Put on fur mittens. Try to play the Christmas carol “Stille Nacht”, from the beginning to the end. Play slowly and as clearly as possible in spite of the mittens.
Since the position for D (re), e (mi) and F (fa) are especially difficult to play, it helps to change the positions of your hands. Your right hand can reach the keys from the opposite side of the normal position.