Hello, and welcome to my letter! To get directly the point: I'm fairly easy to please, I think, but really looking forward to seeing what you come up with. Half the fun of exchanges is seeing other people write things I wouldn't have thought of myself, so please take the suggestions below as guidelines, not the complete limits on what I'd enjoy.
More generally:
Yes Please: Any rating. Gen, shipping, or any combination thereof. Swashbuckling. Story protagonists being dramatically competent in their core skills. Worldbuilding details. Canon-consistent tone and/or voice. Characters the story focuses on being seen by another PoV. Original characters.
No, Thank You: Explicit gore. Non-con (some exceptions noted below). Lifestyle BDSM. Rigid gender roles (outside of those already coded by the setting). Relentless tragedy.
The Goblin Emperor - Csevet
I adore this secretary in every possible way, from his first appearance (where Maia's so impressed by how pretty and graceful and perfectly elven he is) through his general trustworthiness (under every possible pressure!) and off-screen competence (the battle to decide what quarters the visiting grandfather gets!) right through to the way he is a friend of the emperor, in his own way. But I also love all the hints--and explicit details--about his background, with how bad it could have been. Or possibly was.
So I just want more that's focused on him! Any pairing or none is fine by me; he clearly gets along with both high status people (if they'll give him the time of day) and much lower classes, and any variety of shipping of any rating is fine by me. If it's going to get dark and creepy, I'd rather that be with the characters who are already canonically creepy: no sudden dark-and-evil Maia! But dark-and-evil Daco'osmer Tethimar is perfectly in line with canon.
Straight-up competence porn is also good. Csevet battling the forces of OTHER SECRETARIES! Triumphing over paperwork! Sorting correspondence cleverly! Anything of that type.
Imperial Radch - Tisarwat
Oh, our dear Lieutenant Tisarwat who was. The sort of person who uses her first paycheck on changing the color of her eyes to something fanciful, and who has the kind of family who'd indulge her in such desires. I would dearly like to see prequel fic about Tisarwat, covering the sort of person she was, and the sorts of things she wanted, before plot happened to her. Who were her friends, when she had her own friends? What did she want out of her career?
Jupiter Ascending - Advocate Bob
I loved everything about this movie. Action! Fancy dresses! Weird and complicated setting! In general, I especially enjoy worldbuilding for the setting, exploration of galactic society, consequences and all the tricky little details.
But in particular, for this exchange, I'd like to see something about Advocate Bob. Whether it's more crossover with the main plot of the movie, slice of life for him, or some other little plot where he gets to save (or ruin) the day, something specifically about him. (Heck, if you can write convincing shipfic for him, I'll happily read that too.) Bureaucratic competence is a particular delight to me, so something to do with navigating that byzantine system of space paperwork would be especially good.
Wilde Life - Any (Clifford, Oscar, Sylvia)
This comic is still very new, and can be read in its current entirety in under an hour; if you're iffy on something else we happened to match on, I recommend giving it a try.
I like all the main characters! Oscar's level-headed but not unrealistically unflappable, and he tries to be good and helpful, without being some sort of plastic saint. Sylvia's charming, and witty, and I love the way she sprawls in the air while she's hanging around, doing her ghost thing. And Clifford is quite possibly my favorite yet: he's surly and touchy, but for all the right reasons. Who wouldn't be, as a teenager in a situation like his? And for all his snappishness, he keeps doing the right thing anyway.
Prequel stories for Sylvia and Clifford could be particularly interesting. (Separately, I mean, unless you particularly want to give them some connection.) How did Sylvia die, anyway? And we've only seen her be sweet, but what did she actually do to the people she scared off? Why didn't she like them in the house, anyway? As for Clifford, that first encounter with the pack must have been...something. He's clearly not telling the whole story about it. Much less other possible encounters with werewolves before, when he was even younger.
Oscar's harder to write without bouncing off one of the other two characters: a lot of the interesting things about him come in how he reacts to the supernatural, being so entirely mundane himself. But I'd happily see him dealing with other bits of the supernatural--there are surely more in that town--in much the same way he has in the comic.
I would also be totally interested in an Oscar/Clifford shippy story. (I imagine there would be a great deal of awkwardness involved.) UST's also just fine, but however you wanted to run that, so long as it doesn't go terribly dark.