Calm Around People

If your dog is aggressive toward people, don’t even consider him as a service dog.   If your dog is afraid of people you may be able to over come this with training but if you are purchasing a service dog, do not consider a dog that is aggressive or afraid of people.  Even strangers.   
So, how do you teach a dog that gets excited around people to be calm?  Or a dog that is shy around people to become less fearful?  Focus.  You need to train total focus on you, the handler.
Start in a quite place, preferably in your house where your dog is comfortable.  Work on watch and on touch.  You need total focus on nothing but you.  Slowly add some distractions.  Move to another room.  Eventually move to the backyard.  If there is a slip up, move back to where your dog was focused.  Now move to the front yard.  Then the sidewalk and maybe even the park.  Focus, focus, focus on you is the key.
Oh, and you have to be more interesting then the environment, so you’ll need either incrediably tasty treats of the best toy ever.