There is only one acceptable methodology for potty training a dog of any age: positive reinforcement. Traditional advice suggested swatting a dog or rubbing his face in his waste for mistakes in the house, but those techniques do nothing to make the potty training process more understandable for your dog and can actually damage your relationship with him. Keep in mind, dogs don’t view their waste the way we do – to them, pee and poo is pretty interesting! Punishing your dog for going in the house won’t help him understand what he should do instead and might make him afraid to go near you at all, inside or out. Successful potty training requires patience, kindness and remembering that your new puppy is just learning the rules.
I don't teach or recommend so-called "purely positive" methods that allow misbehaving pups to continue misbehaving, instead of teaching them which behaviors are and are not allowed. "Purely positive" is fine for teaching tricks and high-level competition exercises, but NOT for teaching the solid good behaviors that all family dogs need to know, and NOT for stopping behavior problems such as barking, jumping, chewing, nipping, chasing, etc.
Remember that training is an ongoing process. You will never be completely finished. It is important to keep working on obedience training throughout the life of your dog. People who learn a language at a young age but stop speaking that language may forget much of it as they grow older. The same goes for your dog: use it or lose it. Running through even the most basic tricks and commands will help them stay fresh in your dog's mind. Plus, it's a great way to spend time with your dog.
The process is the exactly same for older dogs as it is for puppies; prevent accidents from happening by using baby gates and a crate if possible, create a predictable schedule, learn to recognize your dog’s potty signals, accompany your dog outside and immediately reward for all outdoor elimination, properly clean any accidents and supervise your dog until you’re sure that he understands the rules.