Making environmental changes and being fit is not enough to succeed. There’s still something fundamental remaining: “Mental preparation”; working hard on the other aspects doesn’t do much good if you’re not psychologically prepared.
Remember that studying is a mental activity, so it’s necessary to be psychologically ready to face studying.
You need to be confident about yourself, to be interested and to want to learn, to be optimistic, to set goals and of course, to be able to control your personal problems. How many times has it happened that while you’re studying, you lose concentration because you’re trying to find a solution to something that worries you or makes you mad, like money issues or even problems in a relationship?