What do you want to write about? You don't have to have an answer at the moment, and it will change over the years, but you should think about it.

If you're not sure, think about things that interest you. Start learning about those things, superficially at first. Don't commit to any something, and if something turns out boring and uninteresting, be willing to shift to something else. As you find something that really interests you, learn more. And more.

Find other people who are interested in that thing. Not just people who are interested in writing about it, but also or mainly people who are mainly interested in the thing itself. Hang out with those people, in digital space or meat space or both. Talk about the thing, laugh about it. Hang out with those people in other contexts.

Hang out with other people. Experience as much about the world as you can enjoyably or comfortably stand. Have things happen to you. Write about you experiences, in email or letters or a blog. Maybe keep a journal if it doesn't become a burden. The nice thing about email and letters is that you're mainly just communicating with people in your life, and maybe sometimes you're writing about your thing, but mostly you're just writing for enjoyment.

Learn about writing. Basic grammar and spelling, vocabulary. You don't have to be a technician, but knowing the basics of putting words together properly will keep your readers from being distracted by your language, and they can then become immersed in what you're communicating.

Take some literature classes. Short story writing. Poetry writing. Technical communication. Whatever else interests you. Beyond the mechanics of writing, it doesn't matter too much what specific classes you take, they'll all develop your writing and reading abilities.

Read a lot of good, enjoyable writing.

Learn to observe, maybe learn to draw.

Be interested, and be interesting. Don't bore yourself or others, and don't be annoying, in your life or in your writing.

Listen to people, and especially listen to yourself. Unless you're writing something academic or technical within strict constraints, try to write the way you speak. I personally try to write words that are easy to say together; if the words don't feel good in my mouth when I say them, I change them. I almost never say what I write out loud, but I almost always listen to what it sounds like in my head, to the point of moving my tongue with the words.

Listening to whatever popular music you like, and singing it, can help you develop a sense of what writing "sounds" good and what doesn't. Our species never evolved pencils on our fingers, but we've spoken and listened to each other for hundreds of thousands of years.

Become old. Write about the things you do along the way, and how you got that way. :)

Lots of books and other resources will be recommended to you, and most of them are good. Find one or two that you like, and study them. Ignore the ones you don't like.

The following comes up occasionally on HN. It's about story telling, mostly on the radio, but it's more generally about getting good at your craft. He makes the point over and over that you have to get through the early part when you're not very good, and do it anyway. Most people can't get good without first being not so good in the early days and years.

Ira Glass on Storytelling. https://www.youtube.com/watch?v=loxJ3FtCJJA