hi Wei
first: your notice about your self that you are reserved and nervous is the first step to improve your self.
second: you can use your mind ( specially subconscious mind ) to be relax and calm.
third: the best time to use your mind is the last 15 minutes before sleeping.
fourth: you can use your mind by the power of imangination.
how can you use the power of imagination?
1- see ( imagine ) your self as nervous and notice your body and feelings "how it is bad". and notice the others hate your behavoir and leave you because of your nervous.
2- breathe deeply and then imagine your self as relax and calm and more self confidence, notice your body, your feelings and your thoughs. see how others loves speak to you and you are more and more happy.
practice this training every day and notice the differece. also i advise you to read N.L.P books. they are very useful.