Not that anyone asked, but here are a few things that truly freed me as a writer and ultimately made my writing so much better:
I started writing for myself. Truly writing for myself, not the 'I write for myself' mantra I'd parrot to people while internally still writing with the mindset of 'this is what readers want to see happen'. That shift really happened when I began writing for a rare pair which only previously only had two fics to their tag on AO3. By posting in such a small tag, I was instantly freed from constantly comparing myself and my fics to everyone else. I went from 'this is what readers want, even if it's not necessarily what I want to happen' to 'this is what I want and it's great if other people enjoy it too'.
I let go of the rigid set of arbitrary rules I'd always applied to my writing. The main one was the rule that any chapters/one-shots shouldn't be longer than 3500 words in length. When I started letting myself write until the chapter/one-shot was done, regardless of length it added so much more to my writing, because I wasn't limiting myself to try and tell every story within the same set of word count parameters. Suddenly, I was writing fics that were two, three, or even four times the length of my previously published works and they were infinitely better overall because I was able to fully explore characterisation and plot.
I really let myself get a bit weird in style. I've always written fanfic from third person, past tense as a personal preference. But I started experimenting with other things: a fic where half of the story is written in flashbacks (my favourite fic I've ever written), a fic that's stream of consciousness and mostly freeform (my most well regarded fic by readers), a fic that used transcripts from canon as a way to misdirect the reader until the ending reveals a major twist (readers were so (affectionately) shocked by the ending). While I still mostly write in third person, past tense, the above fics have forever bettered me as a writer.
I stopped obsessing about stats. I used to spend so much time on the stats page of AO3, constantly comparing my fics to other people's. I used to worry myself into a panic spiral by constantly wondering why similar fics by other people had so many more hits/kudos/comments than my works. When I finally stopped checking stats nonstop, I began to truly accept that numbers aren't important. There will always be authors/fics that are more popular than me and that's okay. I realised by constantly thinking 'why don't I have more X' I was subtly turning my nose up to all of the readers who do love my work. I was saying 'You're not enough, I need more' and that wasn't fair to both me and my readers! Now, I don't worry about numbers and instead cherish every single person who reads/kudos/comments on my fics.
None of this is to say I don't ever fret over stats or whether or not readers will like what I write -- but shifting my perspectives and letting go of arbitrary self-enforced rules didn't only make my writing better, but it's also improved the way I approach writing in general, and it's also improved my overall mental health.
