When I first got my Cinnamon GC, she was very nippy.. (she was 7 weeks old so that's when they really start using their beak) took chunks sometimes and most of the time left a nice 'Leila's bitten here' mark.
What I done is had either had a treat in my hand, or I had something like one of her fav foot toys or paddle pop sticks in my hand, and every time she went to bite me, I'd distract her with either the treat/foot toy/paddle pop sticks and it definitely worked, she's not nippy at all anymore. Putting them on the floor is something else you could do, but Green Cheeks love to test you out, so don't scream or anything when your baby nips you.