The theme that I'm writing about is rather serious, you could even call it grim but I want to add a bit of humor to it just because I feel like if I got too serious while writing it that potential readers might be turned off by it. Besides, it can't hurt to be slightly humorous even in dark and macabre situations...
Read Shakespaere and Hitchhiker's Guide. Have a few puns, some witty banter, and use some situational irony. Point out the absurdity of the situation, but never for too long.
I don't know what your theme is. But I will tell you what things are like from my perspective because I have dealt with it before: First of all, I'm by no means a writing expert... I'm just sharing with you the few experiences I've had. But I have written a few "short" novels (the longest one had 50K words I believe) that were mysteries. And I really don't like "gritty" mysteries so I decided to go the lighthearted route by choice. However I was still dealing with murder mysteries and not something silly like "who stole my lunch money?". There were two things I noticed I did that ended up making the story feel more lighthearted yet still keep to the seriousness of being a mystery where people still die left and right. 1. Comedic relief is key: I wouldn't call myself a comedy writer at all. But just stupid things here and there do just fine. I would have a scene where the main characters hang out, blow off some steam, etc, in a way that isn't directly related to the crime. Now, usually I would have it relate somewhat to the story still, but sometimes it didn't. 2. Don't describe in depth the gore of what is going on: I notice a lot of the "gritty" writers are really good at describing a scene in a way that makes you almost feel scared. But if you are trying to also be "funny" you don't need that. I hope this helps.
I am no expert at all, but the first thing that came to my mind is writing a character who provides comedic relief, in terms of he/she not being the brightest person or funny things keep happening to them. Or on the flip side, they could just be a funny person altogether with their personality instead of a "half-wit." Or in shows like Dexter, there is morbid and dark humor that fit perfectly with the tone of the show. Same with True Blood. Actually, almost any dramedy would be a good example. More of them would be Californication, Weeds and Shameless.
I had the same doubt yesterday. I have written a romance, and I've been told that I'm very good at describing feelings, but I feel sometimes the story tend to get a little too serious, when I would like it to be more of a chic-lit-slash-romance-kind-of-story with a little more depth that usual chick-lit. I don't know if that describes the feeling... right now it feels far from chic-lit and more like a romantic drama. it has got funny parts too, but maybe not that many as needed to lighten it up a little.
I just realized one thing on this subject. That sometimes it might be enough to change one word in the right place/sentence to one with a more comic connotation to give the entire sentence a different feeling. You might wanna try this I think it's a good way plus you don't have to rewrite much. you can keep the traditional recipe but add something to spice it up a little. But beware to choose the right place to do this. Some things are better taken seriously and you need to find the right occasion for being funny. this is a quite subtle way if you feel traditional comic conversations or whatever doesn't fit in or if you feel you're not the comic kind of writer.
