Before you begin dog obedience training, choose the best method for you and your dog. Training styles vary, but most trainers agree that dogs respond best to positive reinforcement, such as praise or treats. One common training variation, known as clicker training, includes the use of conditioned reinforcer. There are plenty of dog training books and websites where you can learn about training techniques and determine which best suits you and your dog. When planning out your training methods, don't forget about socialization.
If your dog isn’t giving you an obvious signal that they need to go out (like whining at the door) I suggest teaching them to ring a bell when they need to go outside. Some of the other signs dogs give that they need to go out such as pacing around or circling can be easy to miss if they’re in another room, which is why a noise based signal such as ringing a bell can make things easier.
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.