18 things I've learned in 18 years:
1. YOU. ARE. LOVED.
2. But

not everyone will like you, and it's not always your fault.
3. Don't change for anyone.
4. That said, people are mirrors. Look at how they treat you and see if there is anything you should fix (e.g., an attitude adjustment).
5. Set good habits early and destroy bad habits early.
6. Love, rest, happiness, air, water, and food are necessary. Don't deprive yourself of these.
7. School isn't important. Education is. Learn!
7.5. On a side note, reading is not the only way to learn.
8. Although you shouldn't be a people pleaser, you should strive to have a good reputation among others.
9. Treat others how you want to be treated.
10. Don't expect perfection from yourself or others. People can't be perfect.
11. Even if you can't achieve perfection, always try your best.
12. Just because you fail doesn't mean you're a failure.
13. There's nothing wrong with being nice and there's never an excuse for cruelty.
13.5. That said, sometimes you must be firm with others—especially when it comes to your beliefs and/or safety.
14. You aren't a doormat; don't let others treat you like one.
15. There's always someone who has it worse than you.
16. But that doesn't invalidate your problems.
17. You are rarely, if ever, the smartest person in the room.
18. Listen more than you speak.