How to teach big dogs to be considerate of small dogs size?

I have a great dane and am getting a small dog (12 pounds). He is very considerate of other dogs when socializing. But- just in case I would like to ask anyone who has a big dog and small dog how they got there big dog to be considerate (not step on, not bite, and to be easy playing) of the small dog. I would like to know about how people taught their big dogs that. Also I would like to ask how to introduce a big dog to a small dog. We are getting our small dog second, since we already have a big dog. Does that make a difference? Thank you.