First of all, it is the psychological factor. Too much care about other people's attitudes, this situation, to put it nicely, is too introverted, to put it more seriously, is too strong vanity, afraid of being said "no". Try not to care too much about what others say or how to look at you, perhaps it will be a little more open, the courage will slowly up. In addition, there are physiological factors, if the heart is not good, also easy to be timid, or the body in the lack of certain vitamins, such as potassium deficiency, it is easy to shiver and panic. Eat more bananas, duck eggs and other things rich in potassium.
The most important thing is to be confident, give yourself some confidence that anything can be solved. Then there is a purpose to exercise themselves, forcing themselves to do not want to do but can change their own things, such as speech, part-time salesman ...... of course at first will be very uncomfortable, and do not have the courage to go, but if you do more, get used to the problem naturally solved. One day, you will suddenly realize that you have completely changed.