Depends on the scenario.
If it\'s a case of actually BEING back in time, then that means the timestream is already split from the original and nothing I do to my past self will have any impact on my present self. So I\'d totally use it as an experiement with \"what if...\" and give him all sorts of screwed up advice. With no repercussions, Kep will play dastardly. ^_^
If it\'s just a case of sending a message back and/or having an impact on my present self, then I\'d be more in line with what lono and others have said: very little info given, because those mistakes shaped who I am and I\'m actually pretty pleased with who I am. I would, however, write something like the following to my past self:
\"Dear past self,
You always knew I\'d be in contact with you sooner or later, so read carefully. I can not reveal as much as I\'d like, but you will follow these guidelines. If you don\'t follow these acceptably, I\'ll split the time stream and come back to harvest your organs when I get older.
1) Whenever you\'re depressed, annoyed, or generally frustrated, get on a treadmill and jog, or get on the floor and do crunches, bicycle kicks, or pushups until it goes away.
2) Do not be scared to do something because you might fail. When you feel nervousness well up inside you for whatever reason, acknowledge it, and then do the very thing that is making you nervous no matter how much you might tremble.
3) Also, shave that fucking mustache. There is NO time in which a wimpy mustache is cool. I\'ve checked.
Sincerely,
Your Future Self
PS - I\'m watching you.\"
Kep