I still, very much, classify myself as a young girl. This is more directed to my younger self or a high-school-aged girl. 

I know you (probably) feel like such a grown up right now. All you're worried about is looking older, how well you can contour your face and trying to find a fake id. PLEASE SLOW DOWN. You're at an age where you have so much innocence and so much of your childhood left. Boys are (probably) very prominent in your mind and life right now. They don't care about you, all they want is one thing. I promise. Tone down the partying, stop the drama, start caring about your grades, don't be an asshole to the nice guy because I guarantee you'll be running after him when he's a successful lawyer and the hot guy is still living at home when he's 30. Focus in school. You (probably) don't realise how much it will help when applying for universities and/or colleges. I wish I could go back and change how I behaved in school. Don't let yourself be pressured into doing ANYTHING that you do not want to do. If someone says "we can't hang out if you don't...", you don't need them in your life!! They are forcing you to do things by blackmailing you. Don't be the girl that is a puking, drunk mess at parties. Have a good time, (if you're allowed to) have a drink or two, but please (please, please, please, please) do not let your high school days be the days that you are a drunk mess. PLEASE. You're 13/14/15, not 18 (or whatever the drinking/leaving high school age is in your country). Relationships come and go. Don't be fussed by them. Once you graduate high school, your true friends will become apparent and they're the people that really matter. Skip the makeup, heart breaks and life changing decisions for as long as you can; okay?