Dogs who growl and snap may have true aggressive tendencies or they may be using their actions as a form of communication. Because dogs cannot talk and have limited means of letting their owners know how they feel, they often resort to the only way they know to get their point across. You need to put a stop to this behavior, regardless of the reason, because it can escalate to biting. If you are afraid of your dog or feel he may bite, talk to your veterinarian about a trainer who can help you.
Establish yourself and other family members as the leaders in the family. Don't allow your dog on the furniture unless you invite him up, and make him sit or lie down before handing him his food dish. When he goes outside, make him come to you and sit so you can connect the leash, then walk out the door together, don't let him rush past you.
Control situations that trigger bad behavior. If your dog typically guards his food, growling and snapping at anyone who comes near while he is eating, feed him in an empty room, such as the laundry room. Take him and his food into the room and shut him inside. After 30 minutes, let him out and pick his food dish up so there is nothing to guard. If he growls when he's moved around, such as crating him or getting off the furniture, leave a leash attached to his collar to make it easier to maneuver him.
Correct growling and snapping immediately. Don't hit your dog; a firm "no" should be enough to let him know his behavior is unacceptable.