Being pro-actively social, learning social interaction and dynamics.
Sleeping full nights every day.
Saying no to unhealthy social pressures (ex: smoking weed to fit-in)
Making lists and writing every day.
Journaling. Writing down exactly why I am taking the important decisions in my life, and then later on looking back on that journal and evaluating/correcting my decision making process.
Also wish I had more control over my environment earlier on. Ex: I lived with a cat for 4 years despite being allergic because everyone in my family wanted one. Looking back I think this caused the sinus problems I now deal with. Also my family had terrible nutrition when I was growing up, which I believe impaired my body's height and ability to gain muscle.