The real challenge comes when you have to give the readers something new and unexpected. Refreshment is what makes a story popular and demanding. You can also just build a story on some situation and jot down the humor that arises from the confusion residing in the situation. Another way to ensure the reader's interest in your story is to bring in some amazing twist and turn to a plot that has become somewhat clichéd with time. Have a look at the following ideas to understand what we're trying to imply.
An example for the same would be stories such as Ratatouille, wherein a rat named Remy wanted to be a chef and could talk to the great chef Gusteau in his mind. His journey in reaching the biggest restaurant in the city from the ratholes not only shows a great sense of inspiration, but also the writing style shows a great degree of humor. On the other hand, stories like Madagascar with funny characters such as King Julian, Moto-Moto, and the adorable Penguins, make their serious journey turn into a journey of fun and frolic, making you laugh almost all the time.
Once there was an old man who was flying from Boston to Denver with his cat. The cat was obviously kept in the pet section along with other pets. When the old man arrived in Denver, he didn't get his cat along with the luggage and was extremely worried about it. "I want my cat back or else I am going to sue this airline", the old man shouted at the airline worker. The baggage department was in a chaos and were wondering where did the cat go! Alas, they found the cat in its cage, but to their surprise, the cat was dead. The baggage authorities were already feeling guilty of making their valuable customer upset. "He will blow the airport if he finds out that his cat is dead", an airline employee told another. So they decided to replace the dead cat with a live one. With lots of troubles, the airline finally got the cat back to the old man. The old man looked at the cat and screamed, "This ain't my cat, you morons! My cat was dead and I brought him home to get him buried!"
This is what you call a funny short story idea with a twist! Funny wasn't it? You can also get a lot of interesting ideas just by looking at your daily life and the people in it. What is it that makes you laugh your teeth out? What is it that you think of and can't help but laugh? The best and most convincing funny stories are the ones that are inspired from your own experiences.
Think about it, make characters which are inspired from the real life, create some situations which will make the character act or talk funnily, and create a story based on your imagination. It is also advisable to start and complete the story at a single sitting or else you may end up losing the flow of the story. It shouldn't be a problem for you because this is a short story you are writing and not a huge essay! So start looking around, try and widen your imagination, think of the moments that made you laugh the most, and write all of these in the form of a funny story that turns out to be the best story ever, so that everyone goes on laughing at its narration. All the best!