I'm going to agree with @softest-punk in part, expand on their reply in part, and disagree in part. (And there's another format you can use to structure a story around -- disagree/agree with canon, or something a particular character said, etc.) Here's the part I agree with loudly and wholeheartedly:
If you take no other advice from this list, take this piece: read more. Read widely. Read old books, read new books. Read people's dropped grocery lists. Read amateurs, read professionals, read poetry and lyrics and the backs of shampoo bottles. The more words you absorb, the more you have to draw from when you sit down to write.
Seriously, I've been giving that "writing" advice for decades, and I stand by it as the best writing advice other than "write." If you aren't already reading a wide variety of genres and styles, either do that, or double down on the genre/style you like best and let it inspire you.
Here's the part I want to expand on:
Use an established format. The only one of these still remotely in fashion is 5 + 1 fics, I think (back in my day we wrote songfics and listfics and Very Secret Diaries riffs but I think if you do that last one now Cassandra Clare steals your lunch maybe idk). This I also do all the time, as a way to break the seal on a new fandom. The format is such that you're practically just filling in the blanks. You could do something like this in as little as six sentences.
I love the Five Things [Five Things That Didn't Happen To Character X (& One That Did)] format and, as many such stories are titled "Five Things..." they can be easily found via AO3's search function and you have a trove of stories to browse through and/or further winnow to your fandom(s) of choice.
In my corner of fandom, at least, short-form fic of the drabble (100 words), drouble (200 words), or other arbitrary word-count length is still current — indeed, I just posted a drouble the other day, and my dear friend @petralemaitre posts sprees of short-form prose (and short-form poetry) on the regular. You can even search on "drabble" to find stories tagged that way (though there was at least a while there when people were using the term to mean a short-ish story of any length), if the idea of such a constrained length leaves you wondering what you could even accomplish with so few words.
I'm not going to pretend drabbles are easy, but: 1) the concept of a hard word limit will help you learn to hone your sentences and edit as you go, and 2) if the story gets away from you and winds up being 500, 1000 words, or more? Then you've got a longer story, and that's great too!
Finally, here's the part I have to disagree with:
There's no such thing as 'good' or 'bad' art and you should be suspicious of anyone who tells you there is. The measure of success in art is that it's what you meant it to be.
(emphasis mine)
That first sentence I take no issue with.
However, many creative people find that they feel that even their best, most acclaimed works did not come out as they intended and/or are so flawed that the flaws outshine anything they like about the work in question — and you should take care not to let either feeling, should you experience either about your writing, keep you from sharing what you've written with at least a beta reader or other small audience whose opinion you trust.
Some people seem to have the "all I see are the flaws" response to all of their work, and that's just something they have to push past. Most people, in my experience and across media, feel that much if not all of their work didn't turn out the way they intended at its inception, even if they are pleased with how the work did turn out. So, if you intend a story to begin at point A and proceed through point B to point C, and in the process of writing, you instead wind up proceeding through point И to point Ψ? That's totally okay! Plus, if you want you can still go back and try to write the original idea over again!
tl;dr on this last part: You don't have to be 100% pleased with your final product, nor does it need to be what you intended to create, for your artistic output to be worthy of sharing with the world.
Happy writing!
Any advice for people who have lots of Thoughts™️ about fictional characters but who have not, in the past, enjoyed the act of writing? I was always bad at it in school, which didn't help, and I know ~"you should write it even if it's bad"~ however I am still a recovering perfectionist and this is easier said than done (hence the not enjoying it). Add on top of that that writing fiction is very different from writing a 5 paragraph persuasive essay or whatever else they taught in school, so the little I do know doesn't feel applicable. (I'd just draw fanart instead, but my abilities do not lie there either lol). But I desperately want a way to actually engage in fandoms instead of just lurking in the shadows, and you seem to be quite knowledgeable about writing
Okay so first of all I am SO EXCITED for you because you get to start a new creative pursuit and it's one that comes with a huge community of like-minded people. One of my absolute favourite things in fandom is getting to see people posting their first fic. Truly a magical experience. I am always so so proud of them.
Second, have a quote from Jodi Picoult which is a favourite amongst my beloved writing group:
You can always edit a bad page. You can't edit a blank page.
The trick with writing is that in order to do it, you have to do it. In this way it is similar to the majority of human endeavour.
If you genuinely hate the process then my sincere advice is to not do this. You've only got, like, 100 years at the outside on this little rock. Better not to spend any of them doing things you do not enjoy in your leisure time, if at all possible. Make playlists or reclists, start conversations, take up podficcing, take up fic binding, write meta about your character thoughts, do something congenial to you (and some part of fandom must be congenial to you or you wouldn't like. Be here.)
However. If you do want to write, and you think you could learn to love the process, or at least want to try, here are some inroads you could take a crack at:
Outline your idea rather than trying to write it as a polished narrative and post that. I do this a lot. Sometimes I then go back and actually write the fic, sometimes someone else writes the fic for me, which is delightful. (This looks like "So I'm thinking about a fic in which Aloysius inherits a haunted mansion..." etc.)
Use an established format. The only one of these still remotely in fashion is 5 + 1 fics, I think (back in my day we wrote songfics and listfics and Very Secret Diaries riffs but I think if you do that last one now Cassandra Clare steals your lunch maybe idk). This I also do all the time, as a way to break the seal on a new fandom. The format is such that you're practically just filling in the blanks. You could do something like this in as little as six sentences.
Try epistolary format (letters/texts/emails/post-it notes/notes scribbled in the margins of a notebook/whatever). This cuts all the tricky bits of prose narrative and allows you to focus on the events of a story using a form of writing you are undoubtedly already comfortable with.
Try a retelling. This is what the pros do when they're stuck & it's just fanfic layered with fanfic, really. Crack open a copy of your favourite fairy tale and just rewrite it. Sentence for sentence if you like, with nothing more than names and details changed. Pick a single scene from something you like and rewrite it for The Characters.
There are probably a million more ways to approach this, but the overall point is to get you to start. You simply cannot do a thing without doing the thing. Once you've started, then you can worry about improvement. Or not. You are not obliged to be 'good' at writing in order to do it. Many professional career writers are fucking awful.
A bonus few things I wish I could personally carve into the inside of every new writer's skull:
You are allowed to write more than one story in your life, the first one does not have to say Everything You've Ever Wanted To Say or contain Every Single Idea You've Had. It's probably better if it doesn't, even!
It is orders of magnitude better to finish a very short story that has a complete arc than to get 10% in to an epic and then stop because you don't know how to continue it. If all your writing practice involves writing openings and then stopping, you are teaching yourself to write openings and then stop. Better to write 100 words and have it be a complete story than 10,000 words of introduction.
There's no such thing as 'good' or 'bad' art and you should be suspicious of anyone who tells you there is. The measure of success in art is that it's what you meant it to be.
You cannot possibly please everyone. The person you should focus on pleasing is yourself, because you are the only person obliged to interact with your work. Might as well be fun for you.
Talent isn't real. Anyone who appears to be 'talented' has put a lot of hours of work into doing the thing they're doing.
If you take no other advice from this list, take this piece: read more. Read widely. Read old books, read new books. Read people's dropped grocery lists. Read amateurs, read professionals, read poetry and lyrics and the backs of shampoo bottles. The more words you absorb, the more you have to draw from when you sit down to write.
All that said: please imagine me rolling out the welcome mat and blowing a party whistle while eagerly beckoning you to come in and join the wider writing community.