UnusualReader So many things man. Read more, learn a new language (kids learn things way better), girls, better academic results, work to make money at a younger age, play less games, watch less tv/anime, read less manga, mess with people, blah blah.
But, try not to fantasize too much about what to do if you can restart your life or enter an isekai, alright kiddos? Focus on what's actually happening in your lives right now, the people around you, and whether or not you are living to the fullest.
Insanity is doing the same thing over and over again, but expecting different results. If you daydream about what you'll do if you become a billionaire, get superpowers, etc, yet your actions show that you're wasting your life away, that's insane.
You're the MC in your story, so work hard like the MCs do.
Life lessons from cele~