Training a puppy the right way is much easier than retraining a dog that has learned a bad habit. If you have to retrain your dog it is important to be consistent and patient, they are having to both unlearn and learn at the same time.
Dogs that are as young as four to six weeks old can begin to learn various things. You should start by training them with their name. They should learn to respond to their name. This will happen quickly and naturally if you use their name when talking to them on a regular basis. Once this has been accomplished, dog training can keep going.