Even if you maintain a healthy weight, you may benefit in many ways by improving what you eat -- more energy, more alert mind, better sleep, improved athletic performance, etc. If you are overweight, these points will help you return to a weight that improves your long-term health and short-term performance.
It's not a diet, but a 12-prong approach to a lifestyle that doesn't really limit how much you eat as much as what you eat (though portion control is a good idea, too):
1. Weigh yourself at least weekly and write it down in a monthly calendar (you can use that to record workouts, too)
2. Start with a healthy breakfast every day -- whole grains, fruit, low-fat dairy, eggs, etc.
3. Eat 2 servings (at least a half cup) of fruit daily. Have these readily available -- even cut up and bagged for easy use.
4. Eat 3 servings (at least a half cup) of vegetables (especially leafy ones) daily. Have these readily available -- even cut up and bagged for easy use.
5. Get 25 grams of fiber daily. You will get this through fruit, vegetable, whole grains.
6. Get 1.5 grams of protein per pound bodyweight. This is tough; may require supplement (protein bar, protein shake, etc)
7. Limit sweetened drinks to 12 oz or less a day -- best to eliminate it and substitute a diet drink, but water would be better.
8. Eat 3 meals a day.
9. Eat 2 snacks a day. (Not junk -- fruit, peanut butter, yogurt, nuts, etc.)
10. Exercise at least 30 minutes 5 days a week. (You all get plenty of that.)
11. Get 20 to 80oz of water daily. (1/2 your bodyweight in ounces is good.)
12. Do strength training 2 times a week.
Take one day a week to eat whatever you want but try not to over eat. Best to eat more stuff earlier in the day and lighter in the evening. Also good not to eat anything at least 3 hours before bedtime. Evening snacking will pack on the pounds because when you sleep you are not burning many calories, so they get stored (as fat, of course). I also suggest not drinking too many calories (juice, sugary sodas, beer, alcohol) -- you can consume a lot of calories quickly this way. If you are already overweight, watch the total carbs by focusing more on low-fat protein and leafy vegetables and getting bread, pasta, rice and potatoes mostly out of your meals. Eat colorful foods rather than the white (starchy) ones, which break down quickly into sugars.
Carrying a few pounds less can help you run faster and jump better. Pay attention your fuel.
