You want the secret to becoming a good writer? Here it is: story, style and readability.
If people appreciate your story and like your writing style in the very first thing you ever write, then you are already a good writer.
Chances are though, that one, or more, or maybe all, of the three elements (story, style, readability) will need work before you and/or your readers feel comfortable with your writing.
Learn the rules of the writing craft, then experiment until you know how to break them in a style that is uniquely yours and that your readers enjoy.
What is deemed a mistake for me may work brilliantly for you.
Just one more word of advice: there is no such thing as a good first draft. Good writing is actually good re-writing/editing — absolutely anything can be re-written.