I go to a fairly difficult school and I work 25+ hours a week at an internship. So routine is very important to me, a lot of time Diet, Sleep, and Exercise go to the wayside. It seems I will get a good routine going of eating well and exercising but then I go on break and I loose it.
Diet: Specifically micro-nutrients and more generally a healthy diet.
Sleep: Vastly underrated, sleep deprivation is on par with getting drunk. Consider, long term sleep deprivation can kill you.
Mental Activity: Consider, Solitary confinement can quickly lead to long term mental issues.
Exercise: It's frighting how important this is.
PS: I suspect sleep and diet account for most of the differences in measured IQ in the french study.