These are mostly off the top of my head and to make tagging on AO3 easier for me. I may or may not add more later. Feel free to yoink for yourself, and/or suggest your own in the comments!
Base Level Requirement: If someone goes looking specifically for whatever the tag refers to (ship, character, character dynamic, setting, etc), will they be satisfied by your fanwork, or will they be disappointed? If satisfied, tag it; if disappointed, don't.
AO3 Warnings: Hopefully you know the rules for this! Aside from that, optionally tag any details you think are relevant for either searching or blacklist purposes.
Relationships: Any relationship that is the focus of or otherwise central to the work; if it just gets a passing mention and doesn't impact the plot (etc), you're probably fine to leave it out. Side or background relationships can optionally go in Other Tags.*
Characters: See Base Level Requirement; if someone searching through a specific character's tag were to click on this work, would they be satisfied by it, or would they be disappointed? If you include a lot of characters in a work but they don't have a big/significant part, maybe consider variations on "ensemble" or "everyone", or even just subsets like "Homestuck Trolls" vs "Homestuck Humans", etc.
Setting: Canon compliant, canon divergence, AU (what kind?), modern, modern with magic, etc.
Tropes and Format: Coffeeshop, mutual pining, 5+1, epistolary, sex pollen, etc.
Is there on-screen sex?: If yes, and you've already tagged the work as sexually explicit, then tag which sex acts and/or kinks feature prominently.
Is the ending open or closed? If open, tag Open Ended; if closed, you should be fine to leave it be, or tag "complete".
If text, would you be open to people making podfic? If yes, add "Podfic Welcome".
* I really, deeply, genuinely wish that AO3 had a "background ships" tag field, in addition to ships and characters. Has the potential to save a lot of headaches, but also probably a pain to add at this point.
That's all I've got for the moment; as I said above, I may add more later!
Base Level Requirement: If someone goes looking specifically for whatever the tag refers to (ship, character, character dynamic, setting, etc), will they be satisfied by your fanwork, or will they be disappointed? If satisfied, tag it; if disappointed, don't.
AO3 Warnings: Hopefully you know the rules for this! Aside from that, optionally tag any details you think are relevant for either searching or blacklist purposes.
Examples (may be triggering):
Which parties are underage (one, more than one, all), forced vs coerced vs drugged noncon (etc), type of violence/body part(s) harmed (head/eye/hand/dental/etc), whether the major character stays dead, whether it's a major character you want to root for or are happy to die, etcRelationships: Any relationship that is the focus of or otherwise central to the work; if it just gets a passing mention and doesn't impact the plot (etc), you're probably fine to leave it out. Side or background relationships can optionally go in Other Tags.*
Characters: See Base Level Requirement; if someone searching through a specific character's tag were to click on this work, would they be satisfied by it, or would they be disappointed? If you include a lot of characters in a work but they don't have a big/significant part, maybe consider variations on "ensemble" or "everyone", or even just subsets like "Homestuck Trolls" vs "Homestuck Humans", etc.
Setting: Canon compliant, canon divergence, AU (what kind?), modern, modern with magic, etc.
Tropes and Format: Coffeeshop, mutual pining, 5+1, epistolary, sex pollen, etc.
Is there on-screen sex?: If yes, and you've already tagged the work as sexually explicit, then tag which sex acts and/or kinks feature prominently.
Is the ending open or closed? If open, tag Open Ended; if closed, you should be fine to leave it be, or tag "complete".
If text, would you be open to people making podfic? If yes, add "Podfic Welcome".
* I really, deeply, genuinely wish that AO3 had a "background ships" tag field, in addition to ships and characters. Has the potential to save a lot of headaches, but also probably a pain to add at this point.
That's all I've got for the moment; as I said above, I may add more later!