Allowing play biting is encouraging aggressive play, and can be an issue later in life, especially if you have kids. Dogs naturally play more aggressively than our fur-less selves usually like, so they have to be taught that they can't play that way with humans.
As for training, the most effective method I've found is positive reinforcement. That is, reward with a treat or praise whenever your puppy does what is required of her. For sitting, tell her to sit while placing a hand holding a treat close to her head and a little above it, luring her into the desired position. As soon as she sits, give her the treat. For come, start only about a step away and tell her to come while holding a treat, and give it to her as soon as she walks forward in response. Once she understands that, move further and further away. Most dogs don't take very many repetitions before they understand the connection between the action and the treat. Remember to only say the command once, if it's repeated then dogs tend to think they can ignore it the first couple of times it's said and still get their treat when they get around to listening to you. Use her name along with every command so she knows you want her attention.