Puppie Training?

I just bought a border collie cross from the pound. She is three months old(ish) and her name is Sadie. I'm having trouble with her biting; it's just playful puppy nips but she looks like she s going to turn into a big dog (she might have been crossed with a lab) and so i want the biting to stop. She is going into obedience school soon but does anybody have any tips on how to get her to quit nibbling right away?