First step is to understand that dogs need to chew. They do this for several reasons. Puppies do this when they are teething. Dogs also do this as a way to calm themselves down, to ward of boredom and to keep their teeth clean. So, the most important thing for you is to understand that your little lab puppy NEEDS to chew and will continue to chew all his life.
Once you are very clear about this, there are 3 things you need to do.
1. Provide enough of things for your puppy to chew on: bones, artificial bones, chew toys, ropes etc...Pets stores today carry many varieties of these things. We buy our dog something new each week to chew on. When ever your little fellow chews on his toys or bones, praise him wholeheartedly, so that he knows you appreciate that
2. When he nibbles on you, make a yelping noise (just like a dog would yelp when bitten). Your dog will stop immediately and look at your. Stop playing with him immediately, get up and walk away and don't talk to him for the next half hour. This will teach him that you don't like him chewing on you
3. If he nibbles on anything else (like furniture, shoes etc...), just say a stern NO, gently pull him away, and give him his own chew toy to chew on. Don't yell or shout. If he starts chewing on his chew toy, praise him and pet him lightly and leave him to enjoy his chewing. He will be a happy puppy and you will be happy dog-parents :)