I would tell myself to cherish my time with my dad more than I did because I would lose him young and would regret not spending more time together.

I would also tell myself to get on my bike and ride around the country for a year before starting my career and falling in love and getting married. It's so much harder to do once you're "settled" and have commitments.

I would also tell myself to keep exercising after high school as hard as I did in school. I might not have gained the "freshman 20"(that turned into the mid-life 40) if I had.