Exercise you can control.
Diet you can control.
Circadian rhythm disturbances.... you know, at some time in your career you are going to be very junior and you’ll be getting whatever schedules are left over. Some guys (and gals) are really tolerant of a lot of irregularity in their schedule and some just have a hard time dealing with red eyes and multiple time zone shifts, particularly west to East.
I’ve seen people do melatonin at night, caffeine up the ying-yang in the morning, and every other trick to try to get a good night’s sleep without very much success while some others can pretty much take a four hour nap and totally recharge our batteries. But for people who DO have trouble, circadian rhythm disturbances seem to be what is the least controllable in my experience.