Based on both decent and not so decent replies, I have made some changes to my original post below.
It would seem a whole new kind of AO3 reader/writer is emerging and it is becoming clear not everyone quite understands how the website community works. Here is some basic guidance on how most people expect you to go about using AO3 to keep this a fun community archive that funtions correctly:
Kudos is for when the story was interesting enough to make you finish reading. If it sucked or was badly written, you probably left. If you finished it, you liked it - so kudos.
If you really liked it, you should comment. It can be long and detailed or a literal keysmash. Writers don't care, we just love comments.
No critisism unless the author has specifically asked or agreed to hear it. Even constructive critisism is a no-no unless an author note tells you it's okay. No, posting it online is not an open invitation for that. Many people write as a fun hobby or a way to cope with, among other things, insecurity and just want to share. Don't ruin that for them.
Do not comment to ask the author to write/update something else. It's tacky and off-putting and will probably have the opposite effect than the one you want.
There is no algorithm, it's an archive. Use the search and filter function to add/remove the pairings/characters/tropes etc. you want to read about and it will find you the fics that fit the bill.
For this to work, writers must tag and rate stories. This avoids readers finding the wrong things and missing the stuff they want. I don't care how cringy that trope is in your eyes - it gets tagged.
Character A/Character B means a ROMANTIC or SEXUAL relationship of some kind. Character A&Character B is PLATONIC, like friendship or family.
Nothing is banned. This is an implicit rule because banning one thing is a slipperly slope to banning another and another, until nothing is allowed anymore. Do not expect anyone to censor for you. Because of the tags system, you are responsible for your own reading experience.
People can create new chapters and sequels/fic series any time after they "complete" a story. So it's considered perfectly normal to subscribe, even to a finished story. You can even subscribe to the author instead just to cover your bases.
Do not repost stories or change the publishing date without an extremely good reason (like a complete top to bottom rewrite). It's an archive, not social media. No one cares what's the most recent, only what fits their tag needs.
Try to avoid deleting a story you wrote if you hate it - make it anonymous or orphan it so others can still enjoy it, without it being connected to your name anymore.
It's come to my attention that metaworks ARE allowed on AO3, which is something I wasn't aware of. So if you do post an essay or theory, please tag it as such so others can choose to search for it or exclude it.
The only reason this archive works is because NON ONE PROFITS. Do not link to your ko-fi or patreon or mention monetary gain in any way or you violate the terms and risk having your account removed.
I KNOW there's plenty more I missed but I'm trying to cover most of the basics that people seem to be struggling with.
I invite anyone to add to this, but please explain, don't berate.
