I’ve used index cards (or file cards or postcards) as part of my fiction planning for at least the last ten years. They serve a number of really useful functions.
Firstly, I can jot down on them ideas that I’ve no idea what to do with. I could be out and about and suddenly have this idea of, let’s see, “a man with tattoos that move around his body according to his mood” and I write it down on an index card and can then forget about it until I’ve got some use for it.
Secondly, when bringing lots of ideas together for a novel, I can cover index cards with all manner of concepts, (character traits, plot points, places, themes, etc) and because each of them is on a separate card I can lay them out in webs and patterns, seeing what things belong together. The closest thing I can compare it to is the giant computer screens seen in films like Minority Report where the operator can drag in info, spin it around, couple it with something else or throw it off-screen (although with index cards you can throw it much further).
Thirdly, when all those elements are sorted, the index cards can be put in order (I write little numbers and letter in the corners) and then when put into a pile can be read from top to bottom as a synopsis of the entire novel. There are story-making/roleplaying card games like Once Upon A Time out there that use a similar concept to build stories for instant entertainment purposes.
One of the things I’ve gained from working on Clovenhoof with Heide is using index cards for other purposes. With two writers working on index cards, it’s not only a case of my ideas and concepts that I want. It’s about your ideas that I want, my ideas I want to keep, ideas I’ve come up with but want to throw away and ideas that we’ll fight over to possess. We used a sort of ad hoc trading game to build up the initial characters of Clovenhoof, Ben and Nerys for our novel and it worked really well.
I’m going to a meeting with members of Birmingham Writers Group at Bennetts Bar on Wednesday in which we’ll be discussing ideas for performance pieces for this year’s Birmingham Artsfest.  The particular piece we’ll be discussing this Wednesday is a murder mystery, related  through the voices of the suspects. I think this might be an ideal arena to use a couple of index card games. Crime fiction has certain tropes and clichés and for this, hopefully humorous piece, I want to exploit them to the full. We can spend some time jotting down situations, settings, murder motives, execution methods, stereotypical characters,  stock phrases and red herrings and then play our own sorting, excluding and trading games to not only develop a general plot but also to create characters that each of us can take away and work on.
Independently of Birmingham Writers’ Group, Heide and I will be delivering a couple of Clovenhoof-related slots at Artsfest and hope to be running a collaborative writing workshop or two. If the murder mystery card games work well this Wednesday, I expect we’ll be incorporating them into that workshop.