My blue and gold macaw is an easy bird to handle, she never bites me, and she is just a joy to handle, but bring a stranger to her and its a different story.
I used to think she was being aggressive when she strike out at someone when they would try to touch her, but it has become apparant that it isn't aggression. What it is is lack of trust. Get her to learn to trust a stranger and the lunging stops.
There are a number of videos and books that teach you how to train a parrot, but after your bird is trained, she may need to learn how to accept new friends. I found a video that explains how to train a parrot to accept a stranger.
Check it out:
Teaching Your Parrot To Go To Strangers