Bro, be positive. I am currently a student at LPC, it would be awesome if you are sent here. I think people on reddit have very good critical thinking skills, at least over the average. That gives you an advantage; reddit also has subreddits like r/worldnews which keeps you informed about important things around the world.

I'd say, read http://en.wikipedia.org/wiki/United_World_Colleges#Values and give critical thought to each of the values. Find pro's, con's, think about it's implications on the world

Don't be in a negative state of mind. You shouldn't say "I'm really bad with interviews," believe you can do it well. Confidence is really important in an interview. Greet everybody when you come into the interview room by shaking their hands (it might help!)

BTW: UWC students from USA have pretty high SAT scores; SAT the first round right? Cheers!