I feel that my writing is shaped a lot by my reading.
The Good 
Irony, dry humour. I love the works of Terry Pratchett, Douglas Adams and AA Milne. I like sympathetic, complex characters who are good, but not necessarily
nice, like Granny Weatherwax, Marvin the Paranoid Android, Eeyore and of course Severus Snape. They do the right thing but they don't have to like it!
The Bad 
Teen angst gets on my wick. I hate teen angst. I saw on a forum at another fandom that someone was deeply offended by the term, 'teen angst.' Now, there's a prime example of teen angst. I also find characters who do naughty, bad, evil and nasty things for no reason other than plot requirement irritating. 'Just because' was an adequate reason for me to eat my Brussells sprouts when I was two. I like Brussells sprouts, as it happens, so you're going to have to do better than that, now.
The Ugly 
Song fics. By all that is holy, WHYYYYYYYYYYYY?
I suspect it has something to do with teen angst. Particularly if Evanescence is involved. WHYYYYYYYYYY?
The topic 
So, given the influences, I tend to focus on characters and try to give them good reasons (not necessarily excuses) for what they do, and I like my good guys just a little bit bad. I try not to wallow in angst because it gives me a headache, and if I ever write a song fic, unless it's for something like Monty Python's
Idiot Song or
They're Coming to Take me Away you'll know I've officially gone certifiably insane. (As opposed to merely harbouring suspicions.)
Ironically, I wrote my first fanfic after reading a gosh-awful wallowing teen angsty piece of absolute rubbish on Lori's old archive (I won't name the author although she's no longer around) and figured I could do better than that. It was most encouraging. (I never said I was a nice person.)