Dog guides help their blind partners by walking the person around obstacles, like telephone poles or street barricades. Safety is the dog's responsibility. Dog guides wearing harnesses are at work. People should not pet or otherwise distract a dog guide from his job. Ask permission if you want to pet the dog.
Dog guides are invisible.
At least that's the way you should act if you're wondering how to behave when you meet a blind person with a dog. Dog guides can go wherever the blind person goes. That means restaurants, airplanes, and stores. It's the law. There are several dog guide training programs in the United States.