It's my last year in high school and I'm going to a new school. What are some ways that I can break into the cliques that have already been established? A lot of redditors always say, "I wish I knew in high school what I did now." What are some of those things?

I'm sorry for posting this here. I'm aware of highseddit and askseddit but both are pretty inactive and I've never gotten a response when I've posted there in the past. I'm kind of at the end of the line here...

tl;dr Last year in high school. New school. What do you wish you knew in high school that you know now and how can I socialize with everyone?