Writers need to keep their eyes open and their wits about them at all times. A long day of travel and a middle seat in the back row of an airplane create opportunities to overhear interesting dialogue. Annoying people make excellent victims. A day in a hotel room with no window triggers a setting. People-watching leads to new quirks and habits for our characters.
So here's the thing. The first victim in my next mystery will be a waiter, and I won't say any more about that. I will have a young male suspect who wears his pants with the crotch hanging almost to his knees. One character will rub her nose and sniff a lot, and the protagonist will wonder whether she has allergies...or whether she's a drug addict. And something will happen in a creepy hotel room while the writer is trying to update her blog.
Hmmm. That hits a little too close to home.