If I could turn back time (while retaining my current consciousness) I would do everything differently. I can't say I didn't have good times of a sort, but even during those times I was being used, manipulated, and abused. In part because I was so desperate for friends because my home life sucked and I was neglected and my mom treated me like trash. The only good thing about those times was that I didn't know I was being used or yanked around by these people I called friends, I was just glad to have somebody. I think I had maybe 1-2 actual friends back then, and I fucked up and ended my friendship with them for years because I figured I was going to kill myself, and they had moved on to another stage of their lives anyway.
If I could go back, I would not focus on other people or being "a kind person". "Kind" people get used and treated like garbage, and are expected to always be perfect, always be the sturdy rock people need. But they are also expected to never have needs of their own, and authority comes down on them the hardest for any tiny mistake. Focusing on other people, with the exception of the couple I mentioned, is also a huuuuuge waste of time, resources, and effort; especially when most of them will toss you to the side once you are no longer useful or they find something better. I would instead focus on me. I would do what I wanted, consequences be damned. I would speak up and defend myself. I think it's also possible I would take the chance to run away and start a life of my own with lies and forged documents than stay in a toxic home and school system hellbent on destroying every ounce of my self esteem and breaking me to make me into a wageslave.
People take advantage of the young's naivete and innocence. Good times would have been even better if I had known then what I know now: that other people are not worth one's time or consideration, and that to be happy you need to focus exclusively on yourself and your material possessions.