Dearest Yuletide Authorperson!
First of all, thank you for sharing one of my wonderful, under-loved fandoms! I've been doing Yuletide for years now and it always makes me so very many kinds of happy. The following is just some rambling that I hope may help you figure out what to write if you're stuck, or help you make a decision if you come to a fork in the road in your story, but please feel free to trust your instincts.
A few general notes: The only things that I'm not really a fan of are total and complete crackfic and angst that has no hope of an even somewhat happy ending. Pretty much anything in between is fine, though I will say the more emotional the better. I love the feeling of being sort of emotionally overwhelmed while reading something. That said, it doesn't need to be all "omg the most emotional thing ever", because I do love little domestic, slice of life kind of things, too. In fact what I probably love more than anything is a combination of the two, when some seemingly insignificant, every day moment strikes an emotional chord for the characters. In all of the requests below, higher ratings are more than okay, in fact appreciated, but by no means a requirement for me to enjoy it. If you want to get a better idea of the random sorts of things I like, feel free to check out my tumblr or my Twitter.
On to the request specific things!
Freedom and Necessity - Stephen Brust and Emma Bull: James Cobham, Susan Voight
Things I would particularly love to see in this fandom: epistolary fic, post-canon
Please no: AUs, James denying Susan's agency as a human being, Susan magically becoming the perfect wife and mother
I love James and Susan's banter more than almost anything, and the way their conversations can wander from topic to topic without either of them blinking an eye because they seem to just understand the weird intricacies of each other's brains so very well. Something I am particularly interested in is the ways that they continue to show their devotion to each other despite not being your typical happily ever after married couple types.
I also absolutely love Richard and Kitty and would love to see cameos by them if you feel so inclined, because I feel like they are such better people for having each other in their lives.
Baseball RPF: AJ Burnett/Russell Martin
Okay, this might get kind of long so please don't immediately panic if this is the prompt we matched on. I have a lot of opinions and feelings in regards to baseball, so I'm going to try and answer all the sorts of questions that I would want answered if the roles were reversed -- but! -- I do not think I am in any way always right about these things, nor am I actually that hard to please. I promise. Anything with these two would make me jump for joy. That said, some guidance!
Things I would particularly love to see: the pitcher/catcher dynamic, silly little baseball details, unconventional ways of demonstrating affection and devotion, mentions of Russell's manicures.
Please no: Villainizing the women in either of their lives, bashing other players within the narrative (characters taking issue with other players personally I can deal with if it makes sense, but please only if you feel like it's really necessary to the story you're trying to tell), favoring of outdated traditional stats.
I definitely favor slash with this, no question, but I understand if you can't go that direction. Much of what I'll say holds true whether you're envisioning them as good friends and teammates or as somewhere on the continuum of more than that. The thing I love about these two more than anything is that I can't imagine things ever being particularly simple for them, but I love their devotion to each other despite that. I can't imagine Russell sugar coating it if AJ screws up, but it doesn't mean he doesn't believe in him and I also can't imagine Russell being cruel or dismissive about it, just very matter of fact. Russell I think expects AJ to listen to him when they're on the field, and whether that's in a "dammit, I'm right" way or a "saving AJ from himself and looking out for him" way, or some combination of the two, I'll leave up to you. Either way, he does respect and appreciate it when AJ listens to him. (If you're feeling any sort of kink undertones here, I agree and feel free to run with that if you're inclined.) AJ's Dennis the Menace terrible bleach job and Russell's pornstache are perfect things for them to tease the hell out of each other for, which I can easily imagine them doing. Bottom line I think they are both such total guys, but they're also both capable of moments of surprising insight and sweetness. It's all about contrast and the feeling of always being slightly off-balance with them.
Pan Am: Kate Cameron/Niko Lonza
Things I would particularly love to see: political conversations turning tense but resolving, Niko being simultaneously very old-fashioned and very modern and Kate not sure how she feels about it.
Please no: Glossing over of the very real conflict they must have in their relationship (because of differing backgrounds, Kate's espionage, gender roles in the period, all of it), treating Laura like a dumb blonde, ignoring the importance of the rest of the Pan Am girls in Kate's life
I'll start by saying that this is all based on canon as it stands right this second, and who knows how it might change in the next few weeks, so take this with a grain of salt and go with your instincts if some major bombshell gets dropped between now and the time you write this. I am fairly familiar with the politics of the period, so don't feel like you need to tire yourself out with endless exposition on that regard if it comes up. I like thing to be happy, at least somewhat, but I don't expect a magical fix it, either.