I need help in being myself around others!!! Please!!!?

I'm 15 at secondary school and I'm around my friends and I feel I can just be myself, but then I want to talk to new people but for some reason just can't seem to be myself!!! I really want to be able to just let go and not worry about others opinions of me how can I do this? Any tips or advice would be apreciated!!! Thanks for all the answeres!!!