Start by taking a look at the card. Is it upright or reversed? How does that relate to the image, name, and meaning of the card? Does the image suggest an element? Look at the colors on the cards. Elemental associations are helpful. Here's how you can use them to categorize texts:
Fire: Military Arts and History, Dance, Athletics, Erotic Arts
Earth: Medicine, Animals and Plants, General History and Biography, Spheres and Realms
Air: Science, Philosophy, Music Theory, Mathematics, Astronomy and Astrology
Water: Gates and Spherewalking, Magic and the Spirits, Religion and the Gods, Fiction and Poetry, Songs
Drawing The Usurper always indicates a unique text of some kind: a rare edition, a copy with handwritten study notes or commentary from an important scholar, a book written in a strange language (i.e., the written language does not correlate to the Tongue), or an unexpurgated edition or otherwise variant edition of a well-known work. Draw a second card after The Usurper to determine the actual subject matter.
Here's a worked example:
I draw the Fortune Card, The Creator - Nurture. The card is linked to Earth and Water, and the predominant color in the image is brown, and Earth tone. The Image is of a woman holding a baby. So, I am thinking this card is a text on Midwifery and Child Rearing (i.e.., Earth category for Medicine).
The name of this thick tome is pretty simple:
The Book of the Mother, Being Not a Clan History But a Guide for Midwives and Mothers by Mother Sun.
Description: The Book of the Mother is a common Everwayan text that contains a wide range of lore including information on male and female reproductive biology and how it is influenced by the Fortune Deck, the elements, and stars; charms and methods for becoming pregnant, as well as for contraception; the duties and methods of the midwives; what a mother may expect to happen during pregnancy, childbirth, and the first three years of childhood; the role of the midwife during pregnancy, childbirth, and afterwords; how to create unique given names for children; the proper roles and responsibilities of mothers and aunts; and the proper roles and responsibilities of maternal uncles.