This is a great trick I did this, when they "nip" you hook your index finger behind the large pointy tooth and play a gentle tug of war, do this for a few weeks to get the dog into the cycle, then get a tug toy and hook it behind both teeth and play with that and eventually they stop. You can get some good tug toys with tennis balls and stuff on which are made of special materials that dogs can chew easily so thats also a bonus to discourage this.
I dont personally believe in "training" dogs. I treat my dog like a person to be honest because I dont think its natural to treat a dog like a soldier. My dog is well behaved. Statistics show that training dogs (using methods such as punishment and puppy classes) is only effective 46% of the time. I think there are much better ways of treating a dog. It also creates a nice environment for the dog were the dog feels comfortable and not scared.