Five things my mentor of 3 decades hammered home; five concrete ideas every writer needs to hear, most especially teens.
It's your story, tell it.
Be frugal and artful with your prose.
Practice your art.
Listen to critiques and consider the intent.
Most people mean well. Sometimes they're right. Sometimes not.
Don't let Imposter Syndrome rob you of your dreams. All authors fight it: every single one. It comes and goes, but it's always there. Don't listen to it. Better yet, prove it wrong.
Dream, write, repeat.