Sprinkling some gags into an article is one thing, but add humor to a funny fictional story is a whole new bucket of fish. There are definitely jokes in humorous fiction, but since you're also trying to create atmosphere, normal one-liners often don't slide very well into a story. If a joke doesn't feel like a natural puzzle piece in the whole equation, it's easy for readers to slap you with the "amateur" label. If one-liners must be subtle to be effective, jokes in humorous fiction need to accomplish this twice as much.
The best way to reach that ideal is to let the humor flow from humorous characters. Just take a look at shows like The Simpsons or The Office. These shows fulfill a double-bill - not only do they tell a complete story in a single episode, but each funny bit always seems to come from how their characters react to particular situations. You know Homer Simpson, right? Mostly decent guy, but extremely stupid. In one episode, he decides to teach a class on how to have a successful marriage, and he opens up with this brilliant observation:
HOMER: "Now, what is a wedding? Well, Webster's Dictionary describes a wedding as 'the process of removing weeds from one's garden.'"
Even though Homer is attempting to serve as a knowledgeable figure, his true personality still shines through. That's why he mixes up the definition of "wedding" with "weeding" - he is a true idiot at heart. We laugh because he said something unexpected, and yet in a weird reverse scenario, we totally expect him to say something that dumb. You follow me? It's funny AND in-character - two things humorous fiction must accomplish.
So, how do you make humorous characters that fit nice into your story? Basically, you go ahead and make a normal character - strengths, weaknesses, quirks, the whole slot reel. The real trick between a normal character and a humorous one is how they react to a situation. Humorous characters can have the same logical reactions normal characters have, but usually these reactions are unexpected, exaggerated, or both. All of these reactions still mesh with the humorous character's personality traits, but it's just dialed up to eleven.
For example, say I've got a character who's afraid of spiders. He is totally scared silly of the critters. One day he's in the living room and sees a big fuzzy eight-legger crawling across the carpet. A normal reaction could be something like:
"SPIDER!" Mark shouted. He scampered backwards, leaping onto the couch. "Spider spider SPIDER!"
Now let's see what might happen if he was a humorous character and we allowed him to react in an outlandish way:
"SPIDER!" Mark shouted. He grabbed the corner of the bookshelf against the wall and pushed it onto the fuzzy eight-legger. "Kill it FOREVER!"
But that might be too much for Mark. Remember, even humorous characters need to stay in-character. If Mark wouldn't trash a living room on purpose, don't force him to do it for the sake of a gag. I did say a humorous character can react to something in an exaggerated way, but it DOESN'T have to be wild and wacky craziness. Your humorous character can act quite reserved and still pull out something totally unexpected and hilarious.
That's why planning your characters out first is MAJORLY important. You need to see how their personality factors into the situation first, and from there, you can mine it for the spice. Let's say Mark's a calm guy who prefers to deal with his problems by logic and negotiation. At the same time, he ain't stupid - he knows he can't compromise with a spider. Since a calm guy probably wouldn't throw over bookshelves to kill a spider, let's see how he handles it according to his personality:
Mark climbed up on the couch backwards, watching the fuzzy spider jaunt across his carpet. Okay. No point in screaming. Screaming would just make his voice hoarse now as opposed to later when he would wake up and discover the spider nestling eggs inside his ear. No, best to save it for something special.
"Okay," he said to himself. "Here's what you'll do. For a while you'll pretend the ground is made of lava. Then, when Sandra gets home, you'll offer her the bounty on that spider. She'll have to accept. Otherwise, there's no way she'll be able to buy more worthless furniture this week."
No physical comedy in sight, yet Mark still handles the situation in a funny way, telling himself his plan of action and figuring his friend Sandra can take care of it while mocking her shopping tendencies. Really, if you were to uncolor his language, his normal reaction could slide into any kind of tale about spider hunting. But as you'll see next week, it's color that helps your funny characters really shine. Join me then to find out how.
YOUR ASSIGNMENT: Choose a character you've made or, if you don't have one, create one with some strengths and weaknesses and quirks. Think of how your character might express each part of his personality, but amp it up a little. Maybe Florence loves smoking so much that she keeps a pack in the bathroom as a reward for brushing her teeth. Maybe Johnathan is such a big fan of Star Trek and outdated lingo that he tells people to "talk to the Vulcan salute". Be creative.