Learn as much as you can about life when your young. Not necessarily school stuff but whatch how people interact. Look at the big picture about how life works and decide who you want to be.

Save what money you can and invest it wisely

Focus on school and getting your degree.

Things will be okay, even if they aren’t right now.

Save up money and invest it in a few years.

Always wear protection when having sex.

If you don’t feel good mentally it’s OKAY to look for a therapist and get help.

Exercise body and mind daily.
Listen carefully and explain your truth the same way.
Anything you don't understand, ask. Evaluate. Make up your own mind.
Most things in life are subject to change. Jobs; homes; people; etc. Get used to change. And understand change is the only constant in life.

Never start a job or internship like you know everything already.

And keep learning new things and make new experiences

Do what you want to do and do it soon. Once you get established in a job or a relationship or a house or what have you, it will be too late to, say, backpack around Europe, or run off to Hollywood and try to become an actor, or whatever it is that you dream about doing.

Enjoy being young while you're young, because it passes away in a snap of your fingers, and the biggest regrets will be for the things you didn't do when you could.

Listen more than talk
Do more than expected
Let family and friends know you care

Don't believe most of what you hear automatically. Always check for yourself.

This however will go through one ear and out the other. Because you're 18. It will finally hit you likely around 35.

I wish I was in a position to give advice, lol.

Always try to live in your own way

Delete your SW account.

Don't grow past 26

Be Yourself

What @England66 said. And don't let anyone talk you into joining the sheep herd especially when you know it's the wrong thing to do. Being part of the crowd is rarely cool.

Stop smoking crack