Some writing workshops make you do warm-up exercises, like “Write for ten minutes about a city you’ve visited” or “Reach into the Imagination Basket, take out an object, write about it.”  I can’t say if this kind of shotgun approach is helpful; anything can be helpful when it’s the right tool for your hand. One writing instructor I knew of had people take from the classroom library and use, as a prompt, the first sentence in the first book they found there, which is a kind of sideways bibliomancy, if you think about it, isn’t it?

Do it now.  You don’t need to write about it (unless of course you want to), but let the shelf be your guru today.  Ask a book.