I'm working on a story that I've had a friend help proofread for a few months. The main elements are meant to be serious. However, in my experience, books tend to be boring without a sliver of humor. How do I keep the serious tone to the plot, while also adding bits of humor here and there. Should I use a foil (characters acting as opposites), have something funny happen in a subplot (have a waiter slip on a freshly mopped floor, sending the snails flying into a poor customer's face for instance), or is there another way I could do this? Or should I just put on my Batman Face and forget asking "Why so serious?"