I write epic fantasy novels for young adults. That means I make up a lot of stuff — some of it works, some of it does not. I test my chapters on young adults, particularly my own children, and listen for one thing as they read: laughter. That is the sound of success. If they repeat a phrase aloud and laugh some more then I have achieved perfection! The quoted passage becomes sacrosanct.
It may sound like I’m writing comedy, but humor and laughter are two completely different things. As Dr. Robert Provine points out in his book, Laughter, A Scientific Approach, most laughter is not about humor but relationships between people. We laugh when we see an old friend, or see a behavior in a stranger that is immediately familiar to us. My readers will laugh at an action sequence because they are connecting with something in that scene, not because I’m cracking a joke. Most importantly, laughter is a spontaneous response that indicates they are enjoying what I wrote.
That said, I do absolutely add humor to my stories if it is appropriate to the character. Dark and brooding characters may be sarcastic. Goofy characters will resort to physical comedy. Characters will resort to humor to relieve stress when they are among friends, less so alone. And, of course, there’s nothing wrong with putting a character into an extremely awkward yet serious situation and let the young reader laugh at the character’s mortifying experience. If they didn’t laugh, they didn’t care.
Goethe pointed out: “There is nothing in which people more betray their character than in what they laugh at.” This holds true for our characters and our readers.