Practice. The more you get used to talking to strangers, the easier it'll get
I like shy girl very much.
start trusting yourself.. think of "can do's" instead of can't..
don't care about people around you that what would they think.. and trust yourself, do what you think is right.
Go to the top of a tall building with a megaphone and yell into it "I'M AWESOME!!!! I'M NOT SHY!!!! AND I'M NOT GONNA HIDE MY VOICE, I'M GONNA BE LOUD!!!!!" Or you could try talking to a therapist or someone?