Just sit right back and Listen to every one at the table.
A while ago I ran a short DC Heroes game. The supers were low powered, worked for the government, and were hunting mysterious aliens. I included a handout while the team searched some old moldy gov files. Or perhaps it was mailed to them anonymously? I don't remember. What I do remember is that I provided absolutely no context for the picture. It was a Vietnam era soldier torching a hut that appeared to contain some kind of shadowy creature. Up to this point the team had no idea what they might be dealing with and after this picture they still had very little idea. Here is where things get interesting. As a GM I just laid back on that image and listened to player reactions and speculations. Some of those player ideas most definitely made it into the games story arc. The concept of using player input to build a story is I imagine as old as RPG's. I'm sure DM's very early on heard players say things like, "I bet the duke is the killer!" And then thought "