To get a dog used to wearing a leash, there are several steps you can follow:

1. First, the dog should get to know the leash. Let him sniff the leash and get used to it being placed around his neck or body.
2. Start slowly with training by putting the leash on for a short time and observing the dog. If the dog pulls on the leash or refuses to walk on it, praise him when he does it correctly and give him a treat.
3. Gradually extend the time you leave the leash on. Let the dog walk on the leash and give him lots of praise and rewards when he behaves well.
4. If the dog pulls on the leash, don't pull back or punish him, but simply stop and wait for him to come back to you. Then reward him when he is attentive again and walks by your side.
5. Practice walking on the leash in different environments so that the dog learns that he always has to walk on the leash. If he does well, reward him with treats or a game.

It is important that the training is always positive and that the dog is not put under pressure. It can also be helpful to seek professional help from a dog trainer to ensure that the training is conducted effectively and safely.