Eat lots of fruits and vegetables for nutrient content and fiber.
Take only a moderate amount of calories from the dairy and meat and bean groups.
Eat high fat and high sugar foods sparingly.
Try not to snack too much on foods low in nutrient content.
If you are a vegetarian, pay special attention to your intake of iron, zinc, vitamins B and D and calcium (most people get these from dairy and meat products).
Women and young girls should pay special attention to their calcium intake to insure strong bones throughout life.
Proper nutrition in the teenage years is essential to development -- pay extra attention to what you eat!