Okay, coming from a Senior that graduated last month and just registered for college classes at the University of Tennessee Knoxville (thank goodness that's over, lol)..
High school is a bit ridiculous when you first start. Lots of new things to do and classes to choose from. (Well maybe not as a Freshman, but wait until the next few years. Your choice horizon will broaden.) Here's what helped me when I started.
1.) Make friends with upperclassmen. They're not as stand-offish as you might think and they can be really useful when trying to get information about classes/teachers/etc.
2.) Float around in groups. Don't limit yourself to one group of friends. If you can't do this, MAKE YOUR OWN GROUP!

It's really not hard to find people you have similar interests with if you talk to people. (which brings me to my next point)
3.) Talk to people! Talk to lots of people!! You never know when a random conversation might turn into a lifelong friendship. If you're a little shy, like I was, just try to gather your nerves before talking to someone. Grab a friend who might be friends with them and have them talk to the person so that you can naturally join into the conversation.
4.) Don't freak out about bad grades. If you did bad on a quiz or test, so what? You have others to help balance it out. I started senior year with a 3.7 and graduated with a 3.78 and I probably failed 40% of my tests and quizzes this year. It all works itself out.
5.) Study hard for tests though. Just because you made a bad grade doesn't mean you can slack off for the next test, too. That's when your grades start tanking.
6.) WORK HARD ALL 4 YEARS! This is probably what hit me the hardest. The Seniors my Freshman year told me to do this, but I didn't listen. TRUST ME, it will pay off. When other people are stressing out about if they're going to make a certain GPA for their scholarship or not, you'll be sittin pretty not having to worry about it at all, because your grade is well above the standard for most scholarships.
7.) Have fun. Just because a certain group of kids doesn't like you, doesn't mean it should ruin your whole day/week/etc. Brush it off, have fun with your friends, and live it up. High school was a lot of fun, and I'm sure I missed out on a lot just because I got caught up on stupid things.
When it comes time to graduate, you will want to look back on high school and be proud of what you did and who you were, then look forward to college and hope for the best. You won't be with your friends anymore. You won't have that whole social relationship to rely on if you get stuck somewhere. Embrace high school and be happy where you're at right now. Hope this helped some people out!