Congratulations if you own a grill (the one you wear in your mouth). This is an incredible waste of money but I'm sure the amount of respect you command on the mean streets of your high school hallways was worth the purchase. I'm talking about the other kind of grill.
Guard what you say about others.
This may seem like common sense on the surface but it's one of the easiest bits of advice to ignore. High school, your sports teams, work - all of these places are filled with people with big egos and bigger mouths. You probably can think of several people off the top of your head you do not like and enjoying talking negatively about. You need to fight the urge to get caught up in the shit talking game.
Don't get caught up in the gossip game.
It's enticing to want to talk poorly about people you don't like. However, you will quickly lose respect of your peers and all that shit you talked will come back around to haunt you. It is guaranteed if you share your low opinion of someone to someone else, they will go blabbing all over the school. This will quickly catch up to you, leading to social problems in the most brutal social scene of all - high school. If you have a problem with someone, just tell it to their face.
Don't trust anyone in your social circle.
Besides your absolute best friends, and in high school even they are not a guarantee, trust no one in your social circle in high school. Teenagers will constantly sell each other out just for their own benefit of advancement up the social ladder. If you have a secret you don't want anyone to know, you better not tell anyone. In high school, you are at the point of brain development where you are entirely egocentric - the world revolves around you. This means people will do whatever necessary to benefit themselves first, neglecting all other consequences. I had almost every good friend turn on me at one point in high school. This made me question what "good friend" means. Some of those people remain my good friends today. Notice I said almost, that means that a few stayed loyal. Some people are just cut from a better cloth. If you find friends like this, make sure you keep them on your side.
Listen first, speak only when necessary.
You'll begin to notice that the elite of the popular crowds do not run their mouths. They tend to be very guarded with who they trust and what they say. They also tend to be very guarded with how much they talk. This is because these people have learned to be self disciplined. Think of your words as currency. The more you flood the market with currency, the less value it has. If you take the approach of being a listener and speak only when you have intelligent and thought out words to add, your reputation will quickly grow. People will see you as someone they can trust. This is a very good thing.
Besides your own secrets, you will learn many secrets throughout high school if you know how to listen. Drunk kids at parties, people with less self-control, stoners, emotional girls, all are great sources of information. Once your reputation has grown, more people will trust you with more information. Keep this information guarded. Information is power and leverage. Once you have enough of it, you can command a lot of control over people. The popular crowd tends to engage in activities that are often illegal and immoral. Information about drugs, money, sex, abortions, thefts, steriods, cheating, etc will be entrusted to you. Use this to your advantage when necessary. Just remember, all those people who like to talk shit about other people to you are probably saying the same things about you behind your back. It's just the nature of the beast in high school.