Oh wow, I'm humbled to be asked such a question! I'm no, uh, expert or anything; just to be sure nobody's under any false pretenses, I've only been posting on AO3 since 2018 and only have about 20 fics to my name. But one of the most helpful things I was told before I'd ever posted anything was:
Fanfiction is for you, the writer. Write what you want to write, what you're passionate about, what you want to see happening in whatever fandom universe you're into. You're writing for free, using your talent, your creativity, and your time on worlds and characters you love, so don't let anyone demand more from you, or something different from you. Your stories should never be about the number of likes, kudos, comments, bookmarks, or reblogs you get (side note: you can hide statistics on your personal AO3 dashboard if, like me, you obsess over them and it harms your mental health, so let me know and I'll get the info from my friend again [since it's a little complex and I definitely don't remember all the steps, lol 😅]). Write whatever you feel compelled to write because it feeds your soul. Feeding other people's souls is not your responsibility. You are here (or on the Archive) to serve your own needs and desires, and nobody else's.
I would add that, as always, it is so valuable and so important to be thankful and respectful toward any and all readers/commenters! Your work represents your valuable personal time and effort, and just as no one is obligated to write fic, no one is obligated to read it either--so remember that your fans are also generously giving of their time by reading your work and (hopefully) leaving nice comments. 😊🥰📚✏💜
I guess... as in life, it's important not to take anything for granted in the fic-writing game, not to assume you're entitled to a certain number or percentage of kudos or reblogs. Humility and gratitude are so helpful! If you go into it assuming you're the only person in the world who will like your work, every single kudo, reader, comment, and bookmark is a bonus, a victory, an artifact of appreciation and togetherness! (It always helps me to remember that every kudo has a human being behind it, which is sort of like making a new friend even if you never meet or converse! ☺)
It's easy with fic and in fandom to get overwhelmed or discouraged, particularly when comparing your stats/interactions with others (same as any social media, really), and the advice to "never compare yourself to other people" is meant well but is also not very... practicable. Be sure to keep an eye on your emotional barometer (which gets easier over time as you learn how certain aspects of writing/fandom affect you): step away from it if you need a break, talk about your concerns with a fandom buddy (my dms are always open if you need a backup!), and please don't be afraid to ask for help. Just always remember that you are allowed to be here, you're here for you, and you are in charge of your experience as a writer. If you feel uncomfortable posting something, sleep on it for a day, a week, a year, however long you need to change your mind or edit it to your liking or officially leave it behind. If somebody trolls or abuses you, block them. We're all here for different reasons, but most of us are here for fun and for the love of our fandom(s). As long as writing and posting your stories brings you joy, have at it!
Sorry for the wall of text!! I hope at least some of that is useful in some way, and that I haven't done anything to discourage you. 😳 If anyone still reading has other/better advice, other relevant thoughts to add, etc. please pitch in! 🚀😃🎉✏👍
I wish you all the best in writing, in posting, and in that "real life" thing!! I hope you're able to get/stay happy, healthy, true to yourself, and in love with your fandom faves! 🥰💪🏆💖💜💙💚💛🧡❤ Thanks for the question, and LLAP! 🖖
