I would suggest, if you really want to overcome this problem for good, and get to the core of the problem, that you did psychotherapy. There are visualizing techniques you can use, and you can also try to move from "one-on-one" contact with people, to "one-on-two" until you are really comfy there, and then go on to meeting with three people at the time etc, but to be really effective, try and consider professional help. I do not know how it is where you are from, but the truth is that psychotherapy is not only for "crazy people"... it is for anyone trying to know themselves better and resolve problems in their lives.
Good luck