Which C.S. Lewis book uses the demon Screwtape to give advice about tempting a human?

The C.S. Lewis book in which the demon Screwtape advises a junior tempter is The Screwtape Letters.

Published in book form in 1942, the work is a series of fictional letters from Screwtape, an experienced demon, to his inexperienced nephew Wormwood. Their subject is the temptation of a particular human being, whom Screwtape calls “the Patient.” Lewis uses the imagined correspondence to reverse ordinary moral perspective and expose self-deception.

The letters discuss distractions, pride, resentment, pleasure, prayer, and relationships. Because Screwtape is an unreliable and malicious speaker, his advice is designed to reveal demonic strategy indirectly rather than to serve as straightforward instruction.

Lewis wrote the book in an unusual style for him: he adopted a consistently infernal viewpoint and did not provide a conventional narrator to explain each lesson. The device makes the reader infer the moral meaning from Screwtape’s distortions and failures.