Something that I think developing writers need to learn is that writing is iterative.
If you've ever done computer coding, you'll know that the first time you write the code, it probably won't run exactly how you wanted it to, and a big part of coding is going back and refining bits; changing the order, the structure, looking for missing brackets and semicolons, changing numbers, that kind of thing.
Writing is pretty much the same. You shouldn't expect the first draft to be the perfect version that goes live or to print, because that's not actually normal. Professional writers aren't good because everything they type out is perfect on the first draft; they're good because they go back in and carefully refine the second or third draft to be tighter and really cohesive so that the final result seems to flow effortlessly with great pacing and all come together nicely at the end.
So the only way to really get good at writing is to write something, but do so with the assumption that the first draft probably won't be the final version. Things will get scrapped or changed, sometimes things you actually really like will turn out not to be working, but that's okay because you might be able to use that character or scene in some other story or somewhere else in your plot.
Then, after a little break for sleep or a cup of tea, or after you've written ahead, you can come back, maybe with help from somebody who you trust to respect your writing and who genuinely wants to help you write the best version of your story, like an editor, or a more experienced writer, and you can go through and look for things that could be made better. Is there a scene that drags? Is there something that happens that seems to come out of nowhere because you didn't set up what the audience needed to know for the payoff to make sense? Did a character say something using vocabulary they'd never use? Did you just realise that if you change a detail or two, you can make a whole scene tie into the main themes or a piece of running symbolism way better? You go through and you look for things like that and you make little changes.
Then after you've made the changes and been through many, many drafts, a lot of people won't realise how much work you put in behind the scenes because you'll make it look so effortless, like you just sat down and wrote it all out one day and it all fell into place.