as a worry-wort, who wrestles with anxiety and stress issues, i find that the best way to stay efficient and productive and sane is to not take anything too seriously. in classes.... well, they're just classes... lives do not hang in the balance. in relationships.... well, they tend to come and go so why get too invested when the other person isn't willing? with health.... we all start dying the moment we're born, and it's gonna happen some day- we could get hit by a buss tomorrow, and every day we get out of bed we accept the risk of dying..... without these soothing rationalizations, i tend to err toward being overwhelmed with school stress- obsessing perfectionistic-ally over projects, investing too much in relationships and getting burned, and being almost hypochondriacal toward my health. success for me comes by allowing the universe to do its thing, trusting that whatever happens is meant to be.
to recap: what needs to get done will get done, there's no one to impress or prove anything to, a relationship will never complete you, and you're gonna die anyways.
of course, its one thing to say all of that, its another to practice it.
as far as what makes one generically successful in life? i'd say for some its intelligence, for other's its passion and hard work, though i think the best are those who have both horses hitched to the cart.