I have some great advice for you.
Breathe. If you get nervous, breathe. I know it may sound stupid but it will calm you down in a hurry
If you are trying to make friends, learn when to talk and when to keep your mouth shut. Nobody likes it when they are having a conversation and someone just butts in.
You don't have to be outgoing, I myself am very introverted.
People love humor. If you have a great sense of humor, use it. If not, don't try to force being funny, it doesn't work.
Stay calm and collected, don't worry about upperclassmen messing with you, just stay out of their way and don't do something that's gonna attract their attention to you. Most of them aren't gonna go out of their way to mess with you. Most of them are just whores for attention or have a low self esteem, but that won't make a difference if you piss them off.
Reputations don't go away easily. If someone is messing with you, stand up for yourself.
Stand tall.
High school isn't as bad as it is made out to be. My freshman year was pretty easy going, I made a bunch of new friends, got in some hot water a few times, but now this year is shaping up to be real nice.