Anyways, I read this post back when I thought I was going to do my version of Starship Troopers. I decided to give it a try since I figured I had nothing to lose. Ultimately, the Starship Troopers rewrite didn't work out after all, but the collage experience stuck with me. I got a large cork board, started from the middle, and before I knew it, the damn thing just grew. Science fiction imagery went up alongside various quotes that I felt had a spiritual kinship with what I was aiming for, most of those quotes coming from music I was listening to. I'm still proud of how it turned out, proud enough to show it off below.
What I took away from that experience was that it was an exercise in letting your subconscious manifest itself. You're not getting out plot points or character descriptions. The collage should have a strong connection to the story universe you're writing about - it'd be pretty weird if I did a collage about ponies when I'm writing something in the vein of Heinlein - but in the end, you shouldn't expect any of what's on the board to be something at appears in the book. Of course, that's not to say that the idea shouldn't spark an idea or two. Working on the collage, I had characters from Avatar, Aliens, and Prometheus on there and I began to think about having characters cast in certain molds. For example, how would a cold David-like character interact with a joker like Hudson?
No, in the end, the real goal of a brainstorming collage is to get the feeling of what you're trying to write out of your head and into the daylight. It's supposed to have the unspeakable DNA of your story. Literally, unspeakable. The collage should stir in you whatever it is that got you interested in writing your story in the first place. If anything, it should say, "This is what you want your story to be as good as. This is the field you want to play on."
Sadly, it no longer exists. I have only one cork board, and dismantled the Starship Troopers collage so I could have a go applying the same trick to Undead and Inhuman. Apparently, what works for one project doesn't work for another. Believe me, I tried to make it work, but it just didn't stick this time around so I accepted defeat and moved on to being more productive on prepping for the book in other ways.
Maybe when I finish Undead and Inhuman and move on to the next project, the collage will work again.