I've always wanted to do this myself, and I've finally happened on my opportunity. Last summer I came across a passage in a book I was reading that perfectly fit the underlying theme of a Mrs. Meade story which was then in the planning stages. The thought of what it would be like to use the quotation at the beginning of the story briefly crossed my mind, and then flitted away. But later on it came back to me, and I thought—why not? Since then, apt opening quotations have popped into my head during the outlining of the next few stories, so I've delightedly decided to make them a feature of the series. I'm even going to go back and insert a quotation at the opening of The Silver Shawl—I think I've nearly settled on something from Shakespeare.
Going back to pick one for The Silver Shawl has taught me one thing, though. It's much better and easier to have apt quotations pop into your head and suggest themselves than it is to go looking for one on a particular topic. And for that to happen, you need to have an underlying familiarity with poetry, plays, etc. for your memory to fall back upon. I've started making a little conscious effort to improve myself in that respect. I recently put the complete works of Shakespeare on my Kindle (for $1.99!) and I've been reading a Sonnet here and there over the last few weeks. It's a funny thing about Shakespeare—you can plow on for a while through a tangle of unfamiliar phrasing and obscure meaning, and then suddenly happen upon a line that expresses some familiar feeling almost perfectly. The man certainly knew how to put things. Good poetry is like that—as the narrator of Nine Coaches Waiting puts it, "One always got the same shock of recognition and delight when someone's words swam up to meet a thought or name a picture...Poetry was awfully good material to think with."
In short, I need to read more poetry.