Short films need to have one good idea around which to build them. They need, like any linear story, a beginning, middle, and end (by "linear," in mean in time, since we watch films in linear fashion even when a story is non-linear).
A perfect example of a short film structure is a story joke with a punchline: set-up, complication, dramatic climax, end. Commercials can be great short films, since they are very often built just like this.
But, let me tell you from much experience (of beating my head against a wall), writing comedy is about 10 times harder than writing drama. Comedy has all the requirements of drama (character development, subtext, plot, stakes, goals) plus it's got to make people laugh. There's a reason that many of the most successful comic writers are people who spent years in front of audiences doing stand-up, while there are plenty of dramatic writers who are total recluses.
Whatever you decide to do, expect to fail at it for a while. But still, you should be trying hard to succeed, by making the best films you can.