Often, writers have a hard time pinning down what a common theme in their life is or exactly what resonates with them. This can create blocks when brainstorming ideas. To get around this block, a writer can make a list of his favorite movies, songs, TV shows, books or whatever. Compare all the things on list to identify a common thread that they all share. Do they have a certain way that they deliver their laughs? This should really help to clarify what kind of humor resonates with the writer.
Humor comes from the juxtaposition of two completely different ideas. Irony is the key because people find it funny when they expect one thing and something else happens. Using a random word generator to create juxtaposed ideas can unlock some of the funniest ideas. Another advantage of this exercise is learning that nothing is out of bounds and that when generating an idea quantity is much more important than quality. An idea can be polished, but most people have a tendency to self-edit ideas that they think are bad. However, it's important to never self-edit and just turn out as many ideas as possible.
A writer often draws from personal experience. Using actual situations and changing names, events or locations can often provide a wealth of interesting ideas. A bad date can be an excellent example of a funny situation that can be turned into a great idea for a short film. Using "what if" questions can provide the writer with a wealth of new ideas and funny juxtapositions. Example questions might be: "What if I had said 'x' instead of 'y'?" or "What if 'x' had happened instead of 'y'?" The old adage "write what you know" definitely applies here.
An old technique used by the studios during the classic Hollywood era was drawing stories from actual headlines. People love stories that could have actually happened. These are often fictionalized accounts of actual news stories. There are hundreds of "weird news" stories every day. A writer can make use of these stories by imagining what the story would be like if told from the perspective of the people in the story. Take for example stupid criminal stories, a writer could ask "What lead to the criminal making these dumb mistakes?" or "Why did they do 'x' when 'y' was clearly a better move?"