Choose your friends carefully. Friends can make or break your entire high school experience. If you have to act different to fit in with the crowd you're around or with a certain person, it's probably not the crowd for you. Don't get into something that will mess up your title in school
Boyfriends are not as important as people make them. If you have one, nice. But if you don't that's fine too. A bad relationship can cause a lifetime of trust issues and emotional problems. So get out of that before it's to late because 99% of the time you guys won't be together after high school.
Get involved. Volunteer, join a club, do a sport, help out, etc.I promise, you'll regret it if you don't.It's a good feeling to be on a team or just in a club, even if you don't like the sport or yo're not as good as everyone, you have 4 years to improve. Just have fun, not everything is about competition.
Don't go off on rumors, don't hear something and spread it because it could be false. You never know what the person is going through outside of school.
Remember, who you are in high school doesn't set you up for who you're going to be for the rest of your life. If you mess up, you will get to start over again. You have the rest of your life to be who you want to become. Live it up, you'll miss it when it's over.