Eating healthy. If you drove a race car for a living you would use only the highest quality oil. Racing is similar. I try to fuel with healthy unprocessed foods.
Eating enough. I have seen way too many girls (& guys, but more girls) in sport who eat "lettuce" after a long hard run (or minimally) because they are afraid of gaining weight. If you raced a car for a living would you only put 1/8 gallon of gas in it? NO. You would top off the tank with high quality gasoline.
Extreme Immune Boost multi vitamin was perfect. It is chocked full of antioxidants and covers a balance of everything else I need. I also have peace of mind in knowing Extreme Endurance tests all their products to ensure no banned substances end up in them.
Sleep. The body recovers and repairs itself while you are resting. I typically get 8+ hours of sleep a night. When I am in the middle of a hard block of training I will sleep 9+ hours. I go to bed early. It's possible. Turn off the TV and go to sleep. It's amazing how much better you will feel!
Stress. I try not to do it. I'm human, so I still do. But stress is hard on your body. It increases your likeliness of getting sick. Where possible I try to minimize the amount of stress in my life. Don't sweat the small stuff. It really is not worth it. Life is short. Live it. Have fun.