Hi Laki
I'd tell myself to do the complete opposite of what I wish I had done, in the full knowledge that being a stubborn b@stard I might then finish up doing all the right things.
buy shares in a little company called IBM , or seek out a geeky looking nerd in california called bill gates and marry him -no matter how hard he resists- if neither of these can be achieved don't worry no matter how rocky the road is you will get to the other side ,you will be ok
So, i tell myself at age 21 what the lotto numbers will be for a certain date, guarenteeing myself a win
BUT......i then know that i will only have a short time to enjoy said win, seeing as when i reach the age i'm at now, i will be heading back in time via a portal.
No doubt there will be no way back.....or is this not the Torchwood-type time travelling? ;)