first thing to remember is to let it out. Don't hold your words back. It's better to blurt out anything than stand there looking foolish.
Also remember that you are the man. Say it with me.. "I AM THE MAN" good... Know that you can say what you want whenever the hell you want because YOU ARE THE MAN. Who cares if someone doesn't like what you say, you said it because u felt like it.
Now a good way to start getting social is to ask people about themselves. Try to get inside their heads, find out how the feel on certain things.
Watch the news, watch dave letterman, conan o'brien, jay leno. Observe how they make jokes out of the news and current events. Use some of their jokes if you want, not a lot of high schoolers watch those shows. You'll have things to talk about and you'll become very social after you've tried for a while.
Here's a line that I picked up off of Dave Letterman. I was on a date with a girl who's now about to be my gf.
Me: I was in the train station yesterday and I noticed the US has a MAJOR problem on their hands.
Her: What is it?
Me: Rats. They travel in pacts now. They're like refugees.
Her: *laughs* it's usual to see them in the subway.
Me: No, it's gotton much worse. Yesterday I saw a pact running across the street. One of them broke it's leg.... They shot it.
Her: *laughing her ass off*
there's many things you can learn from dave, he's obviously a great conversationalist and he's very funny. check out the show's site for a few clips and monologues.