My favorite CS Lewis. The letter writing format is perfect for this demon training of how to tempt a human. Plus, it's infused with so much humor.
The Screwtape Letters by C.S. Lewis is a classic masterpiece of religious satire that entertains readers with its sly and ironic portrayal of human life and foibles from the vantage point of Screwtape, a highly placed assistant to "Our Father Below." At once wildly comic, deadly serious, and strikingly original, C.S. Lewis's The Screwtape Letters is the most engaging account of temptation—and triumph over it—ever written.