My take on "what's important" boils down to actionable information for the players, or broad-brush flavor from which specifics can be derived easily in play. For example, available cover in a location is actionable info for the players; the color of the banners in the baron's hall is not. So I make written note of the former, but not of the latter. Or for broad-brush flavor, "richly furnished" is all I need to write for the baron's hall; details like "bright, colorful banners" or "ornate, gold goblets" derive from "richly furnished" and need not be set down in advance. As +Ken H has noted on his blog, improvisation does not mean "just winging it." It means having a well-prepared foundation from which details can be extrapolated. That's the whole idea behind this kind of prep.
So here is how I've been using the cards for my own prep so far:
- One location or NPC per card; locations can be "broad" or "pinpoint."
- Broad Locations (such as a city, a forest, a mountain range, etc.) have a name, a one-line general description and a list of random encounters/events written on their card.
- Pinpoint Locations (a more specific site within a "broad" location, such as a tavern, someone's apartment, a bandit camp, etc.) have a name, a one-line general description, any usable info (e.g. terrain that can be used for cover) denizen stats, treasure, information to be gained in the location.
- NPC Cards have a name, a one-line description, and a list of information or goods to be gained from that NPC, and stats if needed.
I'll talk more about both locations and stats in later posts, but strictly in terms of the 3 x 5 card approach, the I'm finding that the method is working quite well for me. It cuts down on prep time (or conversely it lets me get a lot more prep done in the same amount of time). It also gives my game a more spontaneous and less scripted quality. And as a bonus, it's easier to keep track of what info the players have and haven't gotten without even taking notes, since I can just group together the cards location and NPC cards they've visited and set those apart from unvisited cards.