1. A sense of what the world is like. In my flash fiction stories in From Light to Dark and Back Again, I only have the word count to give a fleeting impression, which is fine. It is just that the fleeting impression has to be strong enough to register with your reader. With a longer story, of course, you can show more but do beware of showing anything that is not absolutely critical to your tale. You don't want to "info dump". Just show your readers what they need to make sense of your story, whether that is one line, one page or what have you.
2. What your character is like. This is best shown in their actions, reactions, dialogue and thoughts. In my flash tale, The Outcome, I don't go into a physical description of Becram, my alien lead, but I do show you his attitude! And for this 100-word story, that is enough.
3. A sense of how the world is run. For my unpublished novel (hope to be working to change that soon, watch this space!), I do show how the government is run. Terry Pratchett in his Discworld series worked out how Ankh-Morpork could operate based on how people got rid of their waste and then how the city was governed grew out of that. You need to pick a place to start to work out to yourself first and foremost how things would work. Then it is a question of working out just what your reader needs to know and which is just for you to enable you to write the story.
4. How needs are met. This can be done lightly. Again in my The Outcome, a few words indicate Becram comes from a highly technological society (so you can imply from that the basics such as food and drink supplies really are not a problem!).
5. Problems! It may sound ironic, but there is no such thing as a perfect world for real, yet alone in fiction, so give it problems it has to try to resolve. For example, does your world get on well with its neighbours? If not, why not? Is it your world's fault or theirs? Have there been attempts to resolve the issues here?