Over the last few months I’ve refined a one-page character background worksheet to fill out when I’m a player or to hand out at the start of a campaign when I’m game mastering. It’s designed in such a way to get players thinking in broad strokes about what sort of character they want to play and what sorts of stories want to tell during the campaign. It’s designed primarily to supplement systems whose game mechanics don’t account for character traits, but in character-driven systems like FATE this sheet can also be used to brainstorm Aspects.
As I’ve discovered in my steampunk Pathfinder game, an experienced GM can plot out an entire campaign based solely on these character creation worksheets (provided you also have a setting in mind). Before every session I look back at these sheets and try to make sure at least one scene, character, or plot hook exists that highlights or ties back to each character’s allies or enemies, goals, or traits. It’s made session prep a lot easier because I can come up with a few bullet points’ worth of scenes for each character and then devote the remainder of my prep time to worrying about mechanical things like adversaries or loot (which are harder to improvise in certain systems).