+1 what April says.
Just make a conscious effort to watch what you eat. Like April, my diet consists of lots of fruits and vegetables, meat, fish, eggs, and nuts. I'm also eating more rice and starchy roots now (training for half-marathon). The point being, stick to foods that are natural and came straight from the earth.
Even if you're busy with schoolwork, you should try to find some time to at least get out and walk every day, or at least a few times a week. Shoot for a couple miles each time, it shouldn't take more than half an hour at a brisk pace. You can even record your lectures and take them with you on an mp3 player (if they're already podcasted, even better).
Good luck! And check back in every once in a while, we'd love to hear your progress
1) eat real food - more vegetables, moderate meat, moderate fruits, less grains, less sugar, less vegetable oils.
2) exercise - moderate intensity cardio, sprinting, heavy lifting, dedicated stretching and mobility.
3) live - relax, de-stress, meditate.
Disclaimer: I'm not professionally qualified to make any formal recommendations. I've just done my homework and I'm my own guinea pig. All of my data, unless otherwise cited, comes from a sample size of n=1 (me).