Years ago, my cousin introduced me to a friend of hers who was a professional writer. When I asked him for advice he said, write every day. Though I appreciated it, I wasn't sure how it would help me. What more should I do so that I could be better at my craft?
Sure, writing every day is important. But if you don't it doesn't mean you can't be a good writer. So, what do I recommend?
For one thing, read books (and short stories) in your preferred genre and books in other genres. Reading in other genres exposes you to different modes of storytelling.
Read books by other types of authors, whether that means reading different races, cultures, genders, etc. You'll get different perspectives and points of view.
Take writing classes when you can – and I'm not only saying that because I present writing workshops!
When writers are starting out, they might not realize the difference between an original idea and an idea that has become a cliché. Another reason why reading is so important.
Be willing to take criticism (when it is constructive) and be willing to evolve. As you learn, you'll become a better writer and you'll learn to trust yourself.
If you want to be a professional writer, understand that being a professional writer is a business. Whether you want to be traditionally published or indie published, you'll have to find a balance between the business and creative sides. If writing is your hobby, then enjoy!