Most of us would go back and mine bitcoin :p

Anyway I would go back and somehow pass my real me some messages how to beheave and how to respond. Because when I look back like 10years from now I done nothing important and missed a lot of good opportunities and today I am struggling a bit but I have learned my lesson.

Positively for me I don't have that smoking habit, it's good that you admit that. I'd suggest that you hang out with people that want to and with once that have successfully quit smoking because you want to feel them and motivate yourself to stop. You can find those people in real life or online on the various forums.