That’s it. Write. You’ll need to learn a lot, but writing is a craft as much as an art – you’ll learn a ton by just writing.
Second: keep writing.
The most common “mistake” prospective writers do is giving up. Learning is difficult. It can be hard. There will be parts where you feel like everything you do is crap. It might even be crap.
Writing crap is not a reason to give up. Writing crap is merely a symptom of your ability to find flaws having out-paced your ability to deliver a story that you will like.
Note the “you.” You might hate your story, but your readers might still love it. We writers are the worst judges of our own ability.
Third: get feedback.
If you want to improve, you need to know what works. It’s not that important to know what doesn’t work – likely most of what you write won’t be the greatest thing you can accomplish (hopefully – after all, you want to improve as your writing progresses.) That’s all right. Focus on what you’re doing right, and do more of that. Over time, you can learn to fill in the gaps in your skill.
And yes, publishing and seeing what sells is a form of feedback.
Fourth: practice trumps talent, content trumps marketing.
This one is a hard one to grasp. The key is that you’re developing. You’re developing a body of work (your backlist, that will sell over years and years) and you’re developing a body of skill that will enable you to write more, and faster, and more engaging stories.
The only way to achieve that skill, is to practice. Deliberate practice if you can manage it, or just pushing yourself in unstructured ways if you can’t. Talent is overrated, practice is king.
As for the marketing, that’s a whole different trap that you’ll fall into once you’ve gotten some books done – most of us want fast success. There is no such thing. Every overnight success I’ve seen has years and years of practice and struggle behind them. So focus on the content, on creating more and more engaging books, and you’ll move forward.
That’s it. Welcome to the writer’s world!
Luck and Persistence!