What are considered to be the most important elements of storytelling in a short film - A suitable soundtrack

A good soundtrack can highlight the mood of the action, either by being parallel to the action or juxtaposing it, which makes it quicker and easier to get the audience more engaged, something a short film needs to do to the audience in a limited time. This is shown in How to cope with death, directed by Ignacio Ferreras, which starts with a very dramatic soundtrack which raises the tension, only for it to change with the action to a very upbeat song, the contrast it very entertaining to watch.