Don't go to online forums.
No, really, I can't say. One thing is difficult. If I could have one sentence then I would be probably more satisfied. "Eat right, workout a lot, move to Portland area, pick up dancing, take school very seriously, read up on skepticism, don't ever lower your expectations and wants/needs, and tell every person everything your parents do."
I would try to pass this information on to me and my parents at age 6-7.
But there is no way one thing would ever help me in my life. It would take a huge list to fix shit. Actually if I could convince myself to convince my parents to seek help because they are alcoholics and depressed then yeah, that would probably make my life significantly better. :/ Again, that would have to be at an very early age like 5-7. The sooner the better, but I mean what can you expect a 5-7 year old to do about all of this really? I couldn't fix shit. So, yeah... Kinda pointless to tell myself anything BUT winning lottery numbers.