1. Have food allergy testing done to know what foods I shouldn't eat, don't digest well, cause inflammation, etc. so I can avoid them.
2. Work with someone from the beginning to develop good training habits, understand what exercises are most beneficial/effective for my personal biomechanics, how to structure a workout and put movements in the proper order.
3. Wouldn't have wasted time cycling. Start out low, stay on and progressively increase dose/rotate or add compounds and check blood work for a year (or so). Gain as much as possible while fresh, then continue blasting and cruising, none of that hormonal rollercoaster business.
4. Learn when enough is enough....training, food, gear, time on, everything.
5. Pay more attention to the importance of sleep/rest/recovery/stretching/flexibility.