First off, let me say that the fact that you're writing me a story is literally going to make my Christmas so please don't feel too stressed, as long as you enjoy writing whatever you write then I'm sure I'll love reading it.
There are things I like in fic: first times, happy endings, angst with happy endings, schmoop with happy endings (are you sensing a pattern?), obliviousness, pining, slow reveals and best friends. I have a thing for seeing how relationships are viewed by people outside of the pairing, and I like the things people show but don't say.
There are things I don't like in fic: unhappy endings, death and non-con. I also don't like humiliation or character-bashing (not that I think you'd do that!) and I have an embarrassment squick a mile wide.
I'm fine with porn or no porn, whatever you're more comfortable with. I'd like slash but I'd be happy with gen.
Now, some fandom specifics:
Tanya Huff - Blood and Smoke series (Lee Nicholas, Tony Foster) - the world needs more Lee/Tony stories! I'd love to see a story where Lee comes out/is outed and how they handle that. I have a secret wish to see what would happen if Lee ever met Vicki and Mike, or what happens when Tony meets Lee's family as his boyfriend (it says in book one that he's already met Lee's mom on set). Or just some plain old demon fighting and magic would rock too!
Emmerdale (Aaron Livesy, Jackson Walsh) - like I said on my sign-ups, I would love something that's a bit cheerier than what's happening on the screen at the moment. I'm definitely not asking you to 'fix' Jackson's injuries if you decide to write something set in the present, but I would like something with a positive feel. I love Aaron's relationships with Paddy and Adam, I love Hazel, I love the whole Dingle clan. Honestly, there's so little Emmerdale fic around that I'd be happy with anything.
Justified (Boyd Crowder, Raylan Givens) - I love Boyd, he's such a complex character and I love how nothing is ever black-and-white between him and Raylan. Something exploring what happens between them after the end of season one would be fascinating or something with the same action/adventure feel of a regular episode would also be great.
Were The World Mine (Timothy, Jonathon) - oh how I love this movie. I don't think you could write anything that I wouldn't be happy with here. I'd be really interested to see something from Jonathon's POV since he so clearly knew he liked Timothy before the magic happened but wasn't ready to do anything about it - how does he feel now that everyone knows? What happens to them after the movie? Anything! :D