I walk a lot so I probably take it for granted. I often notice my greatest insights when they come from outside of myself these days. So I'd say it strikes when I'm listening to others.

We might find creativity by engaging in novel activities. My wife goes on "artist dates" (per The Artist's Way) which are often pursuant of sensory or emotional variety.

Edison (I think) would try to get on the cusp of falling asleep as if association were freer there.