The One-Card Spread. One mistake a writer can make is to reduce a character's tarot card reading into an interpretation of a single card. Focusing on only one card is akin to casting a horoscope based on a person's birth or sun sign, or assigning a character a personality based on hair color.
Most tarot readings involve dealing out about ten cards into what is called a spread. While some spreads have a card designated "the final outcome," not all spreads do. Remember, the final outcome card is always modified by the other cards. Generally, a spread will have cards for the recent past, the present, and a possible future; it will indicate resources and obstacles; and it will have a card that is indicative of the client's character or current state of mind.
An Excruciatingly Detailed Spread. This is the flip side to the previous pitfall. Unless you're writing a guide to giving readings, or a story for a tarot anthology, overly detailed readings are like overly detailed fight scenes. The more detail an author includes, the more likely someone familiar with tarot will spot a mistake (or at least a different interpretation). All the story's reader ultimately cares about is what the cards say and what they mean emotionally to a character.
Over-Specific Cartomancy. The fortune teller deals out the cards, looks at the client, and says, "Tonight, your boyfriend, Steve, will be hit by a red Matrix while he is walking back from Seven Eleven, sipping a Pepsi...." In the stories I've seen this level of detail in, the cards have been cursed to always foretell disaster.
Alas, the cards usually aren't that specific, and if you write them that way, the audience members will wonder why tarot readers haven't won the lottery. A lot.
Take a cue from the Pythia of Delphi and make any advice from the cards obscure (although if a character is convinced the King of Swords in the "obstacles" position is their mean old Uncle Ben, that's an entirely different matter).
Popular Misinterpretations. Probably the most common mistake authors make is forgetting that there are seventy-eight different tarot cards and focusing on one of the more famous ones. Unfortunately, the famous cards are commonly misunderstood because they have emotionally laden and misleading titles.
- The Death Card. Out of all the cards writers choose, Death is probably the most overused and abused tarot card in the deck. If a character has Death show up in their tarot card reading, that does not mean they are going to die; it means that they are going through some sort of transformation, like graduating from school. Repeat after me, "There is no death; only transformation."
- The Lovers Card. Second after Death, the Lovers card is the other most overused and abused tarot card. The Lovers is not, as its name implies, about falling in love, it's about choice. A character getting the Lovers in a tarot reading isn't assured of a good romance or love.
- The Devil Card. This card isn't about Lucifer, Satan, or the powers of Hell. It's about willfully being bound to things material and denying the spiritual aspects of the world.
All Tarot Cards are from the Rider-Waite Deck. Most readers are familiar with the Rider-Waite deck, which is an author's freebie -- but don't forget a quick description if the cards are being used for those readers unfamiliar with them.
Tarot cards go back to medieval times (at least), and they looked differently than the Rider-Waite cards developed around the turn of the 20th century for the Order of the Golden Dawn. Remember to have your Regency, Elizabethan or Arthurian characters use precursors to the Rider-Waite deck. Older decks may have different suits. I've seen medieval (non-tarot) playing cards with suits based on hunting (leashes, horns, etc), and typically older tarot decks call the suit of wands or staves the suit of batons. I've also read a fantasy story where the suits were (I believe) ores, waves, flames, and clouds.
Contemporary decks may feature round cards, feminist themes, Art Nouveau aesthetics, collage decks, cat and dragon decks, and even a deck commissioned by Aleister Crowley (more on him below). There's even a deck based on the Rider-Waite deck where everyone is wearing clothing -- it's the sort of deck one could use to give a reading for one's grandmother and not have her have a heart attack when, say, The Lovers appear. (Assuming she didn't have a heart attack when the tarot cards were first mentioned.)
Aleister Crowley's Thoth Deck. Ah yes; I can already smell the stench of sulfur rising from the deck. Whenever an author wants to show that the tarot cards are evil, the card reader is evil, or that dirty work is afoot, out comes Crowley's Thoth Deck, with the Lust card (his version of the Strength card) right on top. It's the story equivalent of having a bad guy from a movie clack a rifle magazine, sell drugs, or molest children.
If you really want to show that the card reader is wicked, have them over-charge their clients, lead them on with promises of future secrets revealed at the next reading, and make them lie during readings to set the client up to fall in love with a fellow charlatan.
Remember, an ethical card reader will remind a client of the client's responsibility to make their own life choices, so if you want to show an evil reader, make their tarot reading style unethical.
The Tarot Cards Come Alive. This isn't so much wincable as it is has been done before in contemporary fantasy (and comic books), which is not too surprising since many modern tarot guides suggest that students have a focused daydream on a particular card as part of a meditation on its meaning.
Just, um, play nice with the card folks who are naked, okay?