I say this gently for the younger writers out there:
stop putting your own writing down. I'm serious.
scrolling past on ao3 and seeing in the tags and almost back-to-back I see these on two different fics:
I'm holding everyone's hands gently when I say this: PLEASE stop, this doesn't help you nor the people reading.
constantly putting your own writing down isn't going to help you get better, or help you feel more confident—it's going to make it worse.
and I'll let y'all in on a little secret, too: if you, the author, are telling potential readers that you think your own work is garbage, they're probably not going to read it.
"But Jericho, I genuinely suck at writing!" I hear you say. Well listen here, so did I when I was starting out, and that period lasted years to me (in actuality, it was probably a lot more brief). Just keep writing, reading, practicing and learning, and you WILL improve. Have more confidence, you've got stuff to bring to the table that nobody's thought about or had the guts to do.
"But I'm only trying to warn others that my writing is bad!" Let the reader decide if it sucks or not. Don't decide for them if they're going to like what you write or not. a fic doesn't have to be well-written for people to enjoy it.
"But people leave comments telling me my writing is bad!" If you didn't ask for critique or the critique (if asked for) isn't constructive, those people are assholes and you should nuke their comments to hell and forget about them.
"But I don't know how to improve!" Find what works for you. Maybe reading and breaking down the books and works you like will work, or maybe finding people giving out tips, or maybe just a series of trials and errors will work. Just stay writing.
"But I'm only being humble!" that is NOT being humble, that is belittling your own creation(s) and skills. Being humble is acknowledging your skills while also being conscious of ways you can grow/your imperfections, and not letting your ego get to your head. It's okay to say you think you're good at writing and not look like an ass, I promise