The second you leave the house, (in most cases) your parents and siblings are no longer your rivals. They are now the only people in the world who have your backs. Try to make your parents proud of you. Suddenly, there are no more babysitters... Everyone is out for their own good, not yours. Deal with it. Money is VERY important... Make as much as possible without it ruling your life. Research how much being an adult costs before you make any career decisions.
Learn to be humble, even if you are a very confident person and everyone around you seems stupid. If most people frustrate you because they are dumb, don't resent them for it. Instead understand that you have a gift, and that you are blessed. Rise above it and push forward. Be kind to them, but don't let them hold you back.
Let go of any psychological hangover that you may or may not have from childhood. The stuff that happens to people at 6 years old tends to still affect them at 45 years old. You will start to notice how common this is... Research it, Recognize it, deal with it, rise above it.
Pay it forward: The way you treat people affects how they treat others, and so on, and so on. Go to church from time to time, even if you are not religious. It will be good to have a few people in your life who are TRYING to be good people, even if you feel like they are misguided. This, in turn, will be a reminder that you too can try to be a good person.
Sex affects people more than you think. Often times, FWBs, one night stands, etc... means more than you think it does... even if it doesn't seem like it at the time.
Learning to be good at something is often a matter of repetition. If you try something new and it is difficult, try it again, then again, then again... and it should become easy.
Travel. Learn Spanish (if you are American)... If you are a guy, learn how to salsa dance. Embrace more stuff. In high school, looking cool is so important, so there is a tendency to hate things because they aren't cool. If you hate "Uptown Funk" because you are a hipster and you hate mainstream music, you're missing out, because all of the hot women are dancing to Uptown Funk, and you should be too.
Don't eat greasy foods... exercise every day. Staying young longer depends upon you staying in-shape. Get fat and be old by 30. Stay in-shape and be young until you are 50.
Just some thoughts.... hope they help