IG88 and vermilliongirl, welcome to A2K.
It's easier to make small changes that become permanent than to do a complete diet plan that you can stick with for a short while, but quickly fall back to bad habits.
I'm not sure there's one best plan for all teens, but keeping an eye on the junk food is certainly one thing that's easy to spot. One trick is never eat unless you're sitting at a table. Eat whatever you want (try to lean towards healthy choices), but not in front of the television, in the car, at the movies, by the computer, etc. It's amazing how much mindless eating we do and if you force yourself to eat for the sake of eating (hopefully to gain nourishment) and not because you're bored the extra calories you take in will go down.
Another simple change is to force yourself to do some small amount of exercise each day. Watching MTV?, do some jumping jacks. No one needs to know if you think they would laugh. Getting together with a friend?, ask her to go for a walk with you. Sometimes enlisting a buddy to help you stay focused is helpful.
The biggest tip is to stay focused on the big picture. Everyone falls into a bag of chips or cookies occasionally. Don't let that derail you. Just refocus and move forward.
You're welcome to join us on the weight loss club thread here
http://www.able2know.com/forums/viewtopic.php?t=5813&start=3300
We'll give you some support and you can do the same for us.