First off, thank you for offering to write for these fandoms! They really don't get enough attention. In general, I'm a fan of humor, fluff and things of that nature, provided it fits the tone of the series and characters. I'm not too fond of angst or drama, so please be aware of that. If you decide to write smut, I would appreciate an overall lack of watersports/scat, strap-ons/dildos (especially in femmeslash) rape or sex that's only semi-consensual. Really, the more fun both (or all) parties involved have, the better. If you have fun writing the story, even better.
So that's it for the general stuff, now onto the fandom-specific guidelines.
Shark: Danny Reyes, Jessica Devlin, Madeline Poe, Sebastian Stark
I'd love to see friendship and/or romance fic involving Jessica with any of the other three characters listed. The fluffier the better, as long as it's in-character. Bonus points if some of the fluffiness stems from schadenfreude.
Expanding on this, Jessica is my favorite character, and Jess/Stark is my favorite pairing, though I also have a weakness for Jess/Danny and Jess/Madeline, so it's really your choice of who to pair her with, if you decide to do so at all. I'd be just as happy with a genfic involving character interaction and exploration of their interpersonal dynamics and friendships/rivalries. Bonus points if you attempt to capture their voices and match the overall tone of the show. Even more bonus points for including courtroom antics and two or more characters teaming up to make someone else's life miserable.
Leverage: Alec Hardison, Parker, Sophie Devereaux, Tara Cole
I love the whole Leverage team, but the ladies and Hardison are my favorites. Gen and romance (any pairing) both work for me, but either way I'd love it if the focus was more on character interaction and job-related antics. And if you wanted to include Nate/Sophie even though he's not on my list of characters, I'd have no objections whatsoever.
I'm interested in Tara's backtory and how she and Sophie met, even though she's only been in one episode so far and was only herself for about two minutes. Hey, she's played by Jeri Ryan and that's good enough for me. I'm also interested in how she'll mesh with the team and what kind of difficulties might be involved for everyone, especially Parker and Hardison. Or maybe you could write Sophie's point of view on the change and why she chose her specifically. Obviously these are only suggestions, and you're free to write what you will and I'd probably love it just as much. Regardless, I will applaud any attempt to keep it as in-character as possible, as well as any attempt to include Parker being her usual beyond-the-impossible awesome self and Hardison being the nerdy hacker genius that he is. ♥
In Plain Sight: Eleanor Prince, Mary Shannon
I love Mary and Eleanor's interaction on the show, so I'd love to see a focus on the same. Snarky, teasing femmeslash would be lovely, but if that's not your thing then friendship fic would be great, too.
Nothing on the show makes me squee quite like Mary and Eleanor's reluctant friendship/cheerfully mutual hatred, not even Brandi's sweet, good-hearted ditziness or Stan, Marshall, Mary and Bobby D's tendency to go around awesoming at people. Please keep that in mind regardless of whether you write gen or saffic about them (though I'd love you extra hard if you paired them). My only other request is no het, please, unless it's something like a brief reference to Eleanor's poor late husband.
The World Ends With You: Koki Kariya, Uzuki Yashiro
Anything you want to write involving these two would make me so very happy, as long as they're just being them. If you want to pair them up, that's up to you, but I'd be just as happy with gen.
I'd like to see something along the lines of an average day on the job for them (you know, when all of Shibuya isn't going or about to start going to hell in a hand-basket). Or perhaps a story about one of their cherished days off. Really, anything that involves Yashiro and Kariya being their usual jerkass Reaper selves would be great. I don't mind if you decide to pair them up, but I really prefer them as best friends.