I'd probably party a lot harder and in result be more messed up than I am now.
No, but in all seriousness... I might slip in the occaisional "heads-up" in situation from the past, where I'd make the people that mattered to me at that time, more aware of "my situation". Mind you, I'm not saying I'm living my life with regret and am dwelling on the past... the way my life has taken shape now, is probably different from what I envisioned years ago, but it's not worth getting mad or depressed about.
However, I sometimes wonder with the entire "what if..." scenarios (given I take a lot of interest in time travel fiction and alternate timelines anyway). In the past I was in a relationship and my (then) gf thought I was being really difficult to deal with, she did put up with me for years but after a long run we decided it didn't work out. So, what if I said, and knew that "hey, it's not that I want to be difficult, but I have this thing... it makes it kinda hard for you, I'll try to make it easy, so don't take it too personal"... that just gets me to think "nah... she prolly just bailed anyway because she wasn't up for any effort either way". Also, I ended up at a therapist because of a job... would I not ended up there, if I got a different job? I don't know... I might just as well end up there for other reasons, or for a different reason that I thought I ended up there. I mean, I think I ended up there because of the entire company policy, co-workers and stuff like that... what if I ended up there, actually, because I don't have a genuine "work-ethic"... it would land me at the same spot, only with a different experience. Time travel would be cool that way because you could try out alternate routes and learn more about yourself. It's just quite bothersome, that you do age even if you timetravel. I mean... even if you travel back a week in time, you're still dying at some age, and not some date.