Or do a lot of research. Then write what you know. Then learn how to write well.
And that starts with writing; good bad or ugly, competent or all in a muddle, it all starts with writing. And then a bit of sticking to it so that you can learn how to write well.
What I’m getting at here is that if you hope to write for a living some day, start now. Writing is the easy part; writing well just takes a lot of doing. It also requires feedback from readers, who are both your very best friends ever in the whole wide world and your most brutal and honest critics. So you have to love them, and cherish them, and through fair means or foul, keep them.
By golly, there. I’ve said it.
So how do you define “writing well”? Look at the question from your reader’s point of view. Is it ‘readable’? Does the story make sense to the reader, or is it confusing and hard to follow? Are the characters real people or paper cutouts without depth? Are you focusing on character development, or is it all about the plot? Is your writing filled with grammatical and spelling errors? Do you have continuity errors? If you provide dates and times, have you screwed them up, too?
Just how good a writer are you?
You’ll never know until someone other than your mother reads your manuscript. And gives you honest feedback. And you listen to it, and take heed, and correct your errors.
There is no such thing as a thin-skinned writer.
Nobody ever learned anything by doing things right the first time, and I guarantee that no writer ever learned his or her craft without listening to what people (editors, bosses and readers) had to say. There’s a really, really old saying taken right from the Old Testament: “We will do and we will learn”. Note it does NOT say ‘we will learn and then we will do’. Book learning, or sitting in a classroom while listening to a teacher drone on and on never taught anyone anything (go ahead and argue with me – you’ll lose).
You ONLY learn by doing; go ahead and make mistakes – the more the merrier. Beg someone to tell you what you did wrong and then FIX those errors. Make more mistakes and be certain to beg someone else to tell you what you did wrong, fix them and thank those people every day of your life for pointing out your errors.
Your readers, if you allow them, will make you a successful writer. If you can’t take criticism, don’t ever try to write for a living.