I am an absolute believer that to become a good writer, you first must be a bad one. Writing is art and craft, ability and skill; whilst you may have one, you need to learn the other.
You cannot pick up a trumpet and immediately become a master of jazz. Instead, you make a few awkward noises until you figure out how to play it, then learn notes and scales, and delve into musical theory. Until you fully understand both the delivery of music and the principles behind it you cannot even be classed as good, merely someone with potential. What makes writing any different? You may have learned some of the theory and groundwork in school, even developed it in later life, and perhaps have natural talent and flair for it, but those head-starts do not make a good writer.
It may be difficult to hear, but no one picks up a pen or sits down at a keyboard and immediately writes a masterpiece. What comes out is a mediocre first draft at best. That first thing, the initial manuscript; that is the one that no one should ever see. It will have plot holes. The characters will be flat. The writing will be poor. Too much attention will be paid to the wrong pieces of information. It will not be an award-winning book, nor will it be publishable. It will, instead, be that one small step that feels like a giant leap, as it is both.
The first thing you finish—whether it is a story, a poem, an article, a novel, whatever—will be the moment you realise you have become a writer: you aren’t someone who is writing and hoping to finish a draft anymore. You did it. In terms of becoming a writer (or author, or poet) you use a binary, digital measure: zero or one, off or on, no or yes. You have gone from who you were before to being a writer.
Being a good writer, however, is an analogue gauge that assesses a whole three-dimensional spectrum to determine your place on the scale. To get onto it, you need to take that giant leap across the chasm and realise you are a writer. Now you are at the start of a long and difficult and tiring and horrendous and wonderful and incredible and heart-breaking and (most importantly) uphill road that never ends.
Some writers advance slowly, others at incredible pace. The best advice I have ever heard is to make you own mistakes. That’s not to say you should ignore advice or not look to others for help; listen to what other writers have to say as they may prevent you tripping up, but only use what you need to keep yourself moving.
Writing is art, and art takes hard work and love and sweat and emotion and fear and rage and hate and passion and discipline and risk and effort and pain. This is your journey; you need to take it.