Most of the advice we have for writing on AO3 is the exact same advice that we have for writing anywhere else!
Here’s our AO3 specific advice:
Don’t over-tag your fic. Coming up in more searches won’t get you more clicks. You want to get the most relevant searches to get the most clicks.
Tag only your main characters. Absolutely do not tag every character that appears unless its a very short fic.
When you tag a character ask yourself if a fan of that character would feel excited and happy about the amount of screen time that character gets in your fic.
The same goes for pairings. Only tag your main pairing or pairing, and for the same reason.
You don’t need to tag for everything that happens in the fic. If something isn’t a major element of the story, but you still want to warn people about it, put a content warning in your author’s note.
How big is your fandom, and how fast does it move? If you have a very fast moving fandom, you probably want to put out chapters as soon as you’re satisfied with them, in order for more people to see your fic.
However, if you have a slower moving fandom, you probably don’t want to put out more than one chapter a week. It’s okay to sit on chapters for a while if that’s what you want to do.
And finally: write whatever you want! Don’t try to tailor your writing to a specific audience unless that audience is yourself!
If you write it, readers will read it.
edit: oh and of course you can like us your fic!