The best way to rescue a dog from a puppy mill is to work with a reputable rescue organization, such as Best Friends. Although it is tempting, do not buy dogs from pet stores or directly from the puppy mills in an effort to rescue them because this simply supports inhumane and irresponsible breeding practices.
Some rescue groups, such as National Mill Dog Rescue, specialize in taking dogs from puppy mills. Breed rescue groups also frequently get dogs from puppy mills, especially those specializing in popular or small breeds.
Be sure to thoroughly check the credentials of any rescue group you work with, because some irresponsible breeders try to present themselves as rescue groups. The rescue should interview you thoroughly and be knowledgeable and open about both the good and bad aspects of their dogs. Extremely high adoption fees or dogs that are sent to their new homes without being spayed or neutered and vaccinated are other warning signs that the rescue group may not be legitimate.
Once you get your puppy mill dog home, you need to give it special care. Dogs from puppy mills have typically not received adequate training and socialization, so you may have a very fearful pet. Use positive reinforcement techniques to build up your dog's confidence, and be prepared for some setbacks. For very fearful dogs, consult with your veterinarian about whether anti-anxiety medication may help.