2. Eschew the totally evil antagonist (except, possibly, in some horror or monster stories).
Pure evil is dull, unbelievable and predictable. Readers cannot relate to it. Sometimes evil characters devolve into cartoons and become jokes, thus killing suspense or tension. Other times they’re boring: Yeah, yeah, the serial killer who tortured small animals as a child and is now stalking women that remind him of his mother … yawn. One way to prevent a truly dark character from becoming a caricature is to make her a viewpoint character—because no character is the embodiment of evil in her own mind. No one is the villain in his own story. George R.R. Martin did this effectively in his A Song of Ice and Fire series. In its first book, A Game of Thrones, Jaime and Cersei Lannister, the incestuous brother and sister, seem to be evil personified, the characters readers love to hate. In subsequent books, however, they become viewpoint characters, making it difficult not to empathize with them.
If your book’s structure makes it impossible to show the antagonist’s viewpoint, place one of the viewpoint characters in the antagonist’s position and have him try to understand his perspective. Perhaps your heroine is struggling to find day care for her infant while your villain is looking at nursing homes for his aging father. Or they could both lose something dear to them, or confront job-related problems. It could even be something small: Your protagonist could get stuck in a traffic jam, while your antagonist’s flight is delayed by the weather. The point is to show similarity, humanity and an overlap of feelings and experience between the protagonist and the antagonist. This will enlarge the reader’s perception of the antagonist, even if subconsciously.