I was not aware of this at the time that I started writing tarot stories, but apparently "writing using tarot cards for inspiration" is a Thing and there's at least one how-to book on it, that I haven't read. A whole book seems kind of excessive to me. The reason I started doing it is that when I did a bunch of three-card-draw readings for people, it struck me how much the cards formed unique little narratives when you put a few together. I like thinking about characters and setting more than conflict and resolution, so inspiration for the last two struck me as pretty nifty.
The main reason that plot-by-tarot-card works is that each tarot card is just jammed full of ideas and symbols. The symbols vary a bit from deck to deck, but I draw inspiration from the pictures as well as from the text describing the cards. A description of a tarot card (taken from here http://www.biddytarot.com/tarot-card-me
Nine of Pentacles, Reversed:
In its reversed position, the Nine of Pentacles suggests that you may be suffering from financial setbacks or you have experienced a loss due to unwise decisions or foolish actions. Your foundations may be about to give way. If they do, learn from your mistakes and build a more solid and secure foundation next time.
The Nine of Pentacles reversed can also indicate an over-investment in work. You are working long hours at the detriment of your personal life. This is a good time to return to a natural setting (e.g. a forest, beach, mountain or lake) to restore your energies and rejuvenate yourself.
Similarly, the reversed Nine of Pentacles suggests that you may need to release some of your focus on needing to sustain particular income and a particular standard of living, especially if this is coming in the way of other life priorities such as family or relationships. You may think you need the best of everything but really, all you need is your family and loved ones around you. Do not be afraid to take a cut to your income for a short time or to reduce your hours at work, even if this means that you have to eat rice and beans each night for a week to make up for it! It is important that you are focused on what is most important to you. Finances may need to come second and while you need to at least have food on the table, there may be some areas where you can cut back and reduce your dependence on material wealth.
On the other hand, the Nine of Pentacles reversed shows that you want to be able to lead a luxurious life but there is something getting in the way. For example, part of you knows you deserve a beautiful home but another part of you doubts yourself and whether or not you can truly afford it or whether you are going too far and splurging. You want to be surrounded by beauty but you also do not want to be dependent on material possessions for your satisfaction and fulfillment. You do not want to be seen as spending your money frivolously, and so you are reluctant to invest in ‘luxury’.
This gives a bunch of possible conflicts as well as causes for the conflict: the protagonist has financial problems because he's been foolish -- story is about some foolish attempt to make money, and obviously doomed. Protagonist works too hard and has trouble with his girlfriend. Protagonist thinks his family will stop loving him if he doesn't make as much money. Protagonist loves luxuries but is ashamed of this affection so tries to hide it. Or any of these could be problems the antagonist has -- the protagonist has a spouse who drags her into scrapes due to obsessive get-rich-quick-schemes. Etc.
All my tarot stories were short stories, and I always used three cards. I might get a character from one card, a conflict from another card, and a resolution from the third. Often (but not always) I'd use the order of the draw in ordering the events of my story, so the card drawn last would provide the resolution. Obviously, you don't have to do that and you can, for that matter, just keep drawing and discarding until something clicks for you, say. But using the cards I drew kept me from running into 'choice paralysis', where you have so many options that you can't narrow them down to just one.
A random example -- I never wrote this one, just used it to illustrate the method:
Cards: Queen of Coins, upright. Nine of Coins, inverted. Queen of Cups, inverted.
The protagonist is a hard-working, successful warm, affectionate woman (queen of cups, inverted). She is, in fact, working too hard and neglecting her family (nine of coins inverted). This becomes a crisis when her father is hospitalized and she has to help her mother manage affairs, and she realizes how insecure and dependent her mother has become from her father always working and managing everything outside of the home for her. The protagonist sees parallels in the way she treats her own family and resolves to spend more time at home and offline to escape her parents' fate. (Queen of Coins)
A couple sample plots/outlines that I actually used:
A Delight story arc, Citrus:
seven of swords (reversed): mind games, betrayal, getting away with it, puzzles
Eight of Coins: dedication, exacting work, doing a job right.
Knight of swords (reversed): Impulsiveness, enthusiasm, hyperactive, rash
Mirhandrax and Outcast need a MacGuffin reagent. M&O work on complicated plans for stealing, conning, or battling for it. Delight: "Why don't you just trade for it I know some nonprimes who make that?" O: ".... that would be much easier. Yes." Dee gets together supplies for the trip and comes with them, because she knows the nonprimes in question: a family of crefian, giant butterfly creatures living in the Verticals. The MacGuffin is a rare peach-like fruit whose pit is of actual stone; the crefian have a tree that sprouts it. Delight planned to trade them boxes of citrus -- oranges, papedas, kinnows, limes -- for one of the stonefruits, When the adventurers arrive, they find another monster has already tricked the crefians out of their stonefruit tree, so they have to trick it back.
This would be shorter but less plotful without the last. The last also has the "now I need a trick" problem. Two tricks, actually -- one that let the tree get stolen, and one to let them steal it back. The latter might be as simple as "Outcast and Mirhandrax create a distraction while Delight teleports in and out with it."
This was influenced as much by the prompt ("why do they like citrus so much?") and the existing characters I was writing about (Delight and her friends) as by the cards, but I suspect that's part of what you want. In this case, I got my plot from the seven of swords, reversed, which reflected both the central conflict -- "how the crefians got tricked out of their tree" and the resolution -- "how do we get it back?"
This is the outline with which I started "A Guardian's Companion", although I completely went off the rails from it after the first few scenes:
The empress is the guardian's employer, and she's the one who tells him he's too much alone.
The king of pentacles is his dissipated old partner, full of braggadocio, valuing his independence and encouraging his young partner to do the same. "Don't let people's expectations weigh you down."
The king's abundance -- of wine and transitory 'friends' -- distracts the guardian but only makes him feel more isolated, ultimately.
The red serpent, lurking around, vulnerable, needy is his ultimate companion. I'd like the red serpent to be a thread through the story, something the guardian sees without realizing the significance. Maybe the serpent is also alone. I keep thinking of the serpent as a pet, but I think he (she?) would work better as a fellow sapient. Her meaningful companionship is the story's resolution, the Three of Cups.
I think the big utility for me is that I could get a conflict and a resolution from the cards. Even if I ended up doing something quite different from my original idea, having a starting place helped a lot.
There is, obviously, no magic to using three cards; I think using more than one helps because it keeps you from feeling like you're writing The Story of a Tarot Card -- the magic of combining multiple ideas to make New Thing. But I could easily see drawing cards when you're stuck -- "This scene is boring, what would make it more interesting?" or "I need an extra here, what's he like?" or whatnot. Using them to flesh out a complex narrative where you're just weak in spots. And because tarot cards are such archetypes it's not like you end up with the same ideas every time -- there are infinite unique variants on the Queen of Cups or whomever, you're naturally going to adapt the archetype and adds flaws and reflections of setting and story that make your interpretation unique to your story.