I found great success with this:
Leerburg | Who Pets Your Puppy or Dog
My GSD was people aggressive I kept people out of his face. I made the decisions on who he interacted with not him. Today he is a good will ambassador for the GSD in our area. People and kid safe (only under my supervision, this rule applied to kid loving Boxer also) we don't have kids.
Don't know if you do Dog parks or "I thought my dog was friendly folks" but don't ,they can create problems for you to fix. Post 8 has links.
New Dog, Very Challenging