One reason why you might have social phobia is because you fear negative evaluation. Perhaps your self image is negative and you think that other people will also see you that way. Low self-confidence is often a characteristic of persons with social phobia.
The most efficient way to overcome a fear is to face it head on, to essentially do the thing that frightens you the most. If you continually engage in the behavior that frightens you, it will eventually no longer frighten you. It would be an uncomfortable and unpleasant process because nobody likes to feel anxious but facing your fears is the most effective method of overcoming them.
Therapy could help treat this problem. Social anxiety is relatively common and easily treated with psychotherapy and, in some cases, medication. You might also try reading self-help books about social anxiety. They might provide practical ideas that you can try on your own. I hope those ideas are helpful. Please take care.
Dr. Kristina Randle