How do i learn to be more outgoing and social ?

In school I have a group of really good friends, we aren't nerd, and we aren't popular. We're just normal. The thing is, I used to be really really outgoing and popular in elementary school, but once i went to middle school all my confidence just shrivled away and i became very very very shy. Luckily my best friend is in ALL my cles , but i feel weird when none of my friends are in a club i'm in or something, and i just sort of stand in the backgroud and try not to be noticed. When i am alone i don't talk to anyone and keep to myself. I feel like i really want that part of me back that used to socialize with everyone. How can i get my confidence back!? I always feel self concious in a group of people, like everyone is wispering about me and how i'm such an outcast, and am always day dreaming and keeping to myself. The only time in the day i feel confertable is during lunch, when i'm with all my friends at our lunch table, and we laugh and tell secrets, and i feel invincible. How can i be more social. i feel like such an outcast sometimes. please help.