High school is an interesting time in all our lives. Its where most of us really grow up. We go from weird 13 year old barely teenagers, to 18 year old nearly adults. So while you're still in high school it's important to get involved in some kind of group.
Maybe you're a loner and you don't want to have to interact with new people, or maybe you're really outgoing and too busy with plans, or maybe you're just plain lazy. Whatever the reason may be, joining a club or sport or extracurricular activity would be 100% worth it.
You make friends with people you never would've met otherwise; you meet a wide variety of people and are forced out of your comfort zone. When you join a club or sport and stay involved with it all throughout high school, eventually it becomes like a family.
Even if you join a club and things don't go the way you want to and you end up in difficult situations, that's okay. As much as they suck, situations like that are how you grow and mature into a better person. Regardless of how it goes, becoming involved in your high school can only be beneficial for you in the end.
I was that loner who didn't want to get involved with anything but I would never trade my experience I've had in high school for anything else. Marching band especially has helped me feel like I belong in this school and it makes the idea of graduating really saddening, but like I said, I love that I got to be a part of it.
So get out there! Join a club or try out for a sport or do something. You won't regret it!