Cartomancy is, of course, the art of divination by cards. When most people think of cartomancy, they picture tarot cards, or perhaps Lenormand or playing card divination. However, technically, any card deck falls under that heading. I've been spending a lot of time picking at the art of cartomancy lately, as I work on my own divination deck.
I don't think I'd be able to work on the deck I'm building now, though, if I hadn't spent considerable time in college learning a system of divination I refer to as Calvincard (in the tradition of Calvinball, of course.) The principles behind Calvincard are simple: you use what you have to hand, you never read the same way twice, and you make the rules up as you go.
At the time I was working in a gaming store, and so a wide variety of cards from a wide variety of CCGs passed through my possession. I'm pretty sure it was several years before I even read with the same deck twice, though I have fewer cards pass through my hands now and the deck I still occasionally pull out hasn't changed in a while. If you had a bunch of divination cards like tarot, or even collectible trading cards, you could just as easily use them for Calvincard. The rules still hold, though.
I never (knowingly) repeat a layout when doing a Calvincard reading. The cards, their locations and the meanings of those locations are determined by the reading itself. I announce what each card is before I pull it. Then I interpret each card based on the location in the reading, the symbolism of the card, the game mechanic, or something else altogether.
It worked surprisingly well, but it's a serious exercise in learning how to tell what cards mean, not just memorizing a book.
How do you build your own cartomancy deck? It's a process that largely consists of intuition. Calvincard taught me to listen to the meanings of cards in context, which has been invaluable in learning to read properly with my new deck.
The Lost the Sky deck has been an ongoing process of refining the deck - I acquired a variety of cards that were symbolically relevant to the story, and read to see which were useful when they came up in readings. And kept reading. And kept reading.
Feedback was invaluable through the whole process - knowing which cards produce meaningful results for the people I'm reading for let me know which cards worked and which didn't. By cycling through them, I've ended up with a deck full of cards that produce reliable meaning.
While intuition is not the only skill necessary for good cartomancy, it's a necessary one if you're trying to move away from decks that come with instruction books. If you're trying to get away from reading cards in a mechanical, memorized manner, you may find that a few rounds of Calvincard will help you get your head back together.