Your little dog views the world differently. Everything looks gigantic to him. Stop and think about things from his perspective then try to see things from his point of view. Housebreaking is a big issue for little dogs. You must be gentle, patient and consistent, rewarding him when he does the right thing in the right place.
Little dogs feel vulnerable outdoors.
Be sure he has a safe place to relieve himself. Your small dog has feet. Exercise is important to keep your little dog healthy. Little dogs, like big dogs, have to be socialized. Take your little dog to all sort of places and let him meet new people as well as experience new sights and smells.