The tone of the story is also important. If you’re writing something lighthearted you can have more silly jokes without it feeling out of place. In something serious I’ve noticed infrequent subtle humor making me laugh because of how it contrasts the seriousness of the story.

In the First Law books (grimdark) there is a scene where a brutal barbarian finishes quickly during sex and says “say one thing for Logen Ninefingers, say he’s a lover.” Which is amusing but seemed much funnier in the context of the story, who was saying it, and because it used a callback to a Logenism - “say one thing for Logen Ninefingers….”

Another example is when a character with anger issues gets told he’s too intense and scares his love interest. He reacts by thinking something along the lines of “too angry? That is so ridiculous it makes my head want to explode.”