I'm not sure on the actual steps for a safe shoulder carry specifically, but a good place to start for any kind of carrying or actions like that is gaining full trust of the dog. When carrying them normally around they should not be trying to squirm around and jump out of your hands, they should be calm and trust in you. They should also feel secure, the picture looks like he's bracing the dogs back and chest and the dog looks like it's supporting itself using it's legs too. But maybe if the dog can't do this or is injure, get the dog comfortable with being held high up by you. If you got the technique of the carry down, my advice for the steps would be to build the trust your dog has in you, he should be totally comfortable in your arms. Once you have the trust part down try gradually trying out shoulder carrying, maybe starting out crouching low, then going to a full stride or something.