Positive reinforcement is the key to success. A common mistake is to punish your dog during training or become angry. This will only cause confusion. You can try to hold your dog's attention with treats and enthusiasm, but know that it is time to end a session when your dog becomes bored or tired. Try to end sessions on a positive note. Eventually, successful training will be achieved with patience and consistency.
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.