There may be a number of situations in which your dog barks excessively.  We will use, as an example, his continued barking when someone comes to the door.  You can train your dog to bark just a couple of times when the doorbell rings, and then stop barking.  You must teach him an alternative behavior and reward him for the desired outcome.

You may wish to ask a friend to come over and ring the doorbell during your training of the dog.  If your dog is really out of control, you may want to have him leased for the first practice sessions.  When your dog has barked several times after the doorbell rings, wave a treat in front of his face to get his attention.  Then, when he stops barking, praise him and give him the treat.  This process must be repeated until the dog fully understands.

You can also put him in his crate until he settles down.  This serves as a time out when the dog receives no attention at all.  This is punishing in itself to your pet.   Remember, you must be sure to praise him and reward him the minute he stops barking.