if you have a ship you want, put in “character/character”, that is for ships. For duos or non romantic, you do “character & character”. Then you click on the tag that has that once you search. On the side, it’ll show you excludes and includes. You can add or remove any tropes or characters or tags u don’t or want.
it's a bit difficult if you don't have a specific pairing in mind, but you can search by tag if there's a specific trope/theme/kink you're looking for. they have a dedicated tag search (archiveofourown.org/tags/search) that groups similar/synonymous tags together and presents search results in a convenient list for perusal. this can be a bit hit-or-miss, though.
Also, if you write, shorter chapters are preferable for most/standard writing. Keep your tags specific. And ignore the trolls as best you can.
How to read in ao3 I just logged in. If someone could explain. Like how to search for work where to find my favorite genres