This is perhaps one of the easiest tricks and the first one to teach a dog to learn obedience patterns. In addition to being able to demonstrate to friends and family, this trick has other more useful applications: before crossing the street, for example, you can ask your dog to sit while the color of the traffic light changes.
Sit is a short word, sounds good and is a simple command. Before training, you can say it every time the dog spontaneously sits. Later, use treats to reward him when he does so, but always after the command.
Strengthening the training
Even if the dog does it in your presence and obeys your command, try doing it in more places. Take him outside and say “sit”, reward him if he obeys you. Do it in the presence of strangers, in a different context than at home or whenever you can, this way you will be teaching him that he must obey that order whenever you ask him to do so and not only in a specific place. The treat (the reward) should be removed gradually and replaced by another gesture of approval.