1 - Eat Breakfast! Even though you may be in a rush and only want something small, or nothing at all, breakfast is an important part of your day. It's important to get in as many of the vital vitamins as you can in the morning. This will pump you up for anything the day throws at you.
2 - Water. It's very important. People say 8 glasses is the right amount, but if you can't get em all in don't worry too much about it. Water cleans your system. Other drinks cannot offer this benefit to your body.
3 - Skipping meals. A lot of people try to skip meals in hopes that if they can just skip that one meal, they won't take in as many calories. Well you're wrong! Chances are that even though you thought you had a good idea, it will backfire. Most people end up over-eating later in the day.
4 - The food groups! Okay, I'm not gonna rhyme them all off to you cause im sure your school has pounded them into your brain. Anyways, try to get as much as you can from them all without exeeding the reccomended amount of portions. Too much can be bad, same as too little. You don't need to plan your meals around the guidelines, but keep them in mind.
5 - Excersize... yeah yeah, get off the couch! As much as some of us (myself included) loathe working out, it is VERY good for you. Don't overdo it! Try to get as much cardio in as you can in your day. 30 minutes a day is ideal, but you can change that to fit your schedual. Always stretch before AND after any workout, it keeps you from getting cramps.