Decided to combine two random elements: one open for interpretation and more determinant of mood, theme, etc, the other more specific.
Ended up choosing:
1) A card from the Beasts of Albion deck. For those not familiar (which I imagine is most), these are not so much event-divination cards as self-divination cards. As the name suggests, each is an individual animal representing a specific attribute and a number of other qualities.
2) A random sentence from a book. I'll probably use the last one I finished for a bit, just for simplicity. Whether I keep this up or find another method depends on how fast I read. This has been "not very," of late.
Further restrictions set for myself: exercise needs to be around 200 words, at least that much and preferrably not much more. The meaning of the card needs to be used, but I can also use the signifying animal directly. The sentence can be assumed as the beginning or the end of the exercise, but isn't counted in the total. (And not the middle - that's so I can more easily substitute if I decide to write the whole story.)
Exercise also doesn't necessarily have to be at the beginning of the story, though I seem to be notoriously bad at writing random middles and ends. Wasn't always that way ...