Sleep and proper nutrition are important of course, but sometimes these may not be enough. I play tennis five days per week and without taking supplements I wouldn't be able to handle the intense exercise and all the pressure. So currently I'm using Aceformula (aceformula.com) as energy booster. Coffee works as well but I have trouble falling asleep after drinking it. Also, I take vitamin B and get my vitamin C from lemons (I'm one of those weird people who eat lemons without adding sugar or any other sweetener).