Sleep
If you take away just one piece of instruction from my article, let it be this: get good sleep.
Why? Sleep disruption leads to insanity.
Seriously. In his book, "The Depression Cure," Stephen Ilardi, Ph.D. writes:
When laboratory rats are experimentally deprived of slow-wave sleep [a deep, restful form of slumber] for several days at a time, their brains start to malfunction and they become seriously ill. Humans react in much the same way. After just a few nights of slow-wave deprivation, most people report intense, aching fatigue. After a few more days, they begin to feel physically ill. They also start moving and speaking more slowly. Many people even complain of a sensation of physical pain (even though they can't quite tell where it's coming from). In this sleep-altered state, mood turns despondent, social interest disappears, thoughts turn negative, appetite becomes erratic, and concentration wanes. In other words, with the disappearance of slow-wave sleep, the core symptoms of depression quickly emerge.