What do you regret in life?

Hey there, I was wondering what you regretted in your life such as misbehaving in class, not caring about certain oppurtinities that would've helped you with life, or even rejecting offers that were huge.

I'm going to 7th grade, and I just wanted to know if there's anything that I should not do, or should do. In addition to that, I also want to know people's experiences.