How to make my dog stop growling?

my dog is a very good dog but protective over my family. when my friends come over he growls when he is in his cage because we are playing. and when i go to hug my mom, which he is very protective over, he growls and nips at me. its our fault for antagonizing him but i there any way to make him stop. maybe some tips to reconstruct him to be nicer.he is still young and easy to teach so anything will work...please help....