Put education first no matter what.
Don't let others dictate on how you should live your life.
3.Don't listen to gossip. Remember when you are not around, you will be the subject of gossip.
Put up healthy boundaries and enforce as needed.
Stay away from toxic people.
Just because someone falls in love with you, doesn't mean you have to let them guilt you into taking over your life. It's okay to say "no thank you."
Also, when a relationship turns sour, it's okay to trust your gut and leave. The sooner the better, especially if there is abuse. If he smacks you around, leave as soon as possible. It does not get better, and you do deserve better. It is far better to be alone than to be stuck in an abusive or controlling relationship.
If you know how you want to live your life, cut out the people who keep you from it, and just live your life. Just because there is an expectation in our society that everyone needs to be paired up, doesn't mean everyone has to. Live your life how you want to.
"Have a seat, 18yr old me. We need to talk"
"Yes, there is fine."
"Now...18yr old me, you're going to make about a dozen good decisions in your life. All the rest will be shit. Don't be so stupid."
"I'm not stupid!"
"Yes, you are and you're also going to be bald by the time you reach 40 so be ready for that."
"No way, dude! Not gonna happen. Hey, will I get laid a lot?"
"You'll have sex with your girlfriends, a few one-nighters and eventually your wife."
"But you'll fuck that up too. She's gonna divorce you"
"Pffft! Her loss."
"Yours too. It's gonna hurt like hell."
"I'll get another one. Me likey the ladies, dude!"
"You'll be in your 50s. It's a lot harder than it'll be in your prime."
"Old dude, you don't know me. I got it all covered. Your problems are YOUR problems. Don't make em' mine. Now, I gotta go. There's this new thing starting called MTV and I wanna check it out. Later, oldtimer!."
I told you he was stupid.
I'd tell her to maximize opportunities and stop slamming doors in her own face. I'd tell her that life is short and love is precious. I'd say to have more sex with more people. I'd say you're stronger than you know and you're going to need it all, but it will be worth it in the end.