Hmmm, interesting. It seems like the trick is to just take "Be Specific" and reverse it - go up the abstraction ladder until you reach a more general area, one which is small enough to easily jot down a lot of general categories. Then take each of those and be more specific.

Basically, you're stuck in one "branch" of the "abstract tree", and if you just climb back to the root of the tree, you can then explore other branches. (I'm a programmer, so my trees are naturally upside down. For everyone else, apologies for the mixed directional metaphor :))