Canon is a priority while writing, but there are fanon tropes I fall for, definitely. I love coffee-obsessed!Draco and rentboy!Draco, for instance. I don't think I've written those examples yet, but I would love to.

I slash source material all the time in my head, nowadays. Fandom has definitely affected how I watch/read fiction. Even if I don't further explore a pairing myself, while I'm watching/reading something, I'll think, oh those two have a great dynamic in this scene. I bet they have loads of shippers. :P And when it comes to pairings I already ship, I'll go back and pay special attention to their scenes. One time, I re-watched all of Firefly just to count the Inara/River scenes! xD