How to overcome shyness?

Well, at my new school, I'm doing fine. I'm hardly shy at all.(Because there's only like four people in my class along with me.) But I'm talking about when I go back to my regular school in eleventh grade. It's just so many kids. So many "cool" kids. And I was in the "stupid" o "uncool" kids. I didn't have any Friends back in that school. Pretty much because I was so shy, and I don't know what else. I try to say hi, but I just can't get the courage. Anyone know how I can overcome it?