The Facts of Life... Or Advice I'd Give High School Freshman

1. You cannot control how other people treat you. You can control how you treat them. I see this thing happen a lot: A kid gets treated like a "freak" or an "outsider" by his/her peers. And then s/he decides to embrace that label, and, rather than just being comfortable with who they are, they distance themselves from others. The number of times I've seen a kid with stringy hair, wiry glasses, and anime shirt treat a blonde girl with a short, floral skirt and an Abercrombie jacket like crap, just because he assumes she's already labeled him a certain way, is remarkable.
2. On a related note: be nice to people. I know that it's super hard to be nice to some people sometimes. But life is hard for everyone. So make it a little tiny bit easier on yourself and the people who are around you and just be nice. Almost everyone likes nice people.
3. Don't feel guilty about your "guilty pleasures." I unironically watch soap operas. I have a lot of affection for the boys in One Direction--I might only know two of their songs, but I like them. I love ABC Family Original Holiday Movies. I probably know all of the words to all of the songs on Hilary Duff's first album. Same goes for the first JoBros album. And I don't feel guilty about any of that shit. You know why? Because those are all things that make me happy. Yes. Belting out, "I TOOK A TRIP TO THE YEAR 3000 THIS SONG HAD GONE MULTIPLATINUM EVERYBODY BOUGHT OUR SEVENTH ALBUM WE OUTSOLD KELLY CLARKSON" makes me happy. You should only feel guilty about pleasures if they hurt someone. Which means stop feeling guilty about and/or denying that you like pop music or Disney Channel shows or styles that went out of style two decades ago or whatever.
4. Think about what you say before you say it. I know, everybody and their mother gives that bit of advice, but people still say really ignorant, sexist, and racist comments all the time. So, I figure it's advice everyone still needs to hear. 
5. Keep at least three spare feminine hygiene products in your bag. If you don't have any spare tampons, you'll inevitably get surprise attacked by menstruation at a Starbucks. If you only keep two spare tampons, they will inevitably unwrap themselves in your bag rendering them useless. Plus, if you have extra feminine hygiene products, you will get to save the day when your friend got surprised attacked by menstruation at a Starbucks. Or you will get to befriend other women who frantically run out of the stall, look around, see you standing there, ask timidly if you have a spare tampon, and then look at you like you're the answer to a prayer when you hand one over. 
6. Hang out with people who you like who you are when you're hanging out with them. Do not spend your time with people who bring out mean or catty or gossipy sides to you if you don't like being mean or catty or gossipy. 
7. Hang out with people who don't want to change you. Personally, I've never been much interested in spending my time with people who say, "I'd like to see you drunk." You want to know why? I wouldn't like to see me drunk. I wouldn't like to be drunk. So I'd like to spend my time with people who want to see me sober.
8. Don't ever catcall people. People don't like getting catcalled. It's intimidating and nerve wracking. Also: that's not going anywhere. Seriously, could you imagine talking to a couple and asking, "Where'd you guys meet?" And then have them say, "Well, it's a funny story, actually. I was walking to the store and he drove by and saw me. So he rolled down his window and called out, 'that's a fine pair of legs you got there'." It was love at first harassment.
9. Do your work. Getting around doing your work requires a lot more effort than it's worth. If you're supposed to read a book: read the book. If you watch the movie, you have to worry about the differences between the book and the movie. If you get the Sparknotes chances are you'll be missing important information. Just read the book. Muddle through. It'll be fine. If you're supposed to write a paper: write the paper. I'm serious, all the weird techniques people use to not do the assignment are obvious and dull and require too much effort. 
10. Don't be too hard on yourself. Making a mistake every now and then won't bring down the foundation of the world. You can fail a quiz or show up late or forget about your family dinner and everything will be fine. You just have to take responsibility and move forward. Everything will be okay.