Throughout elementary school, each grade would put on a musical during the year. Our music teacher always told us that if we got nervous, to look at the red exit sign. She said that we wouldn't be able to see anyone else looking at us if we did. It's worked for me; I had terrible nerves the first time I performed after elementary school but I looked at the sign and they went away.
The best way for me was to put myself in situations where I was forced to be infront of people. I joined activities in my church where I had to dance and sing by myself. I always volunteered to do the morning announcements in front of my church every Sunday and that really helped me. Now I can get up and speak infront of people without hesitation.