I'm going to discuss nipping and chewing first. Some of this information might already be known to you. After that I'll give you some tips that I have used with stubborn pups.
When a dog is chewing and nipping on people the best method is to say “NO’ make a cry of pain and most puppies will respond and stop. For those that don’t respond, you will need to redirect his nipping or biting to an appropriate object. If you are playing and he nips, you want to do the same and then stop playing with him. He should learn soon that if he nips, playtime is over. Some puppies learn earlier than others and most do not totally learn not to nip and chew on you until they are 4-5 months old.
Another thing that you will want to do is try and teach children that may be around your puppy not to make high-pitched squeals and run. To a puppy or dog, high pitched noises mean play time and it is a natural instinct called prey drive to chase after a running object. You may want to keep a leash on your puppy at all times so you can easily give a quick tug for a correction when he is doing something that is not allowed such as nipping or chewing. You also need to remember that corrections are worthless if not done when the behavior is occurring. You can not correct a dog if you find something chewed. You can only correct him when he is actually doing it.
Here are some great sites on bite inhibition.
An important thing with a pup that has been taken from its mother early is socialization. Once your pup has completed his shots at around 16 weeks old, you will want to enroll him in Puppy obedience classes. Of course you can work on sit and come at home but class will be a chance for your puppy to interact with other puppies and learn from the experience. He will probably be in contact with older dogs as well and gain more dog social skills as well. You should also have him around a varied group of people so he is comfortable with all people whether they are children, adults, elderly, white, black, and green. etc. A well socialized dog is less likely to become a problem dog.
Now I have had some stubborn cases that I've worked with. For nipping at the ankles and pants legs, I adopt an exaggerated walk that keeps my heels moving throughout the walk making sure they are raised high in the back and not stopping because a pup runs into the heel. They usually stop attempting to go for the ankle or pants when they run into the heel of your shoe a few times.
If they don't respond to the above methods concerning hand biting, I then take an alternative responsed. This has to be done nicely and not hard. Instead of pulling your hand away, you push it a little farther in which sometimes will trigger the gag reflex. At first they think its an accident, but when it happens a few times, they realize that they can't get away with biting anymore.
I hope you find this information helpful.