I've undertaken to write a book with 50 tales, one per page.
It is hard going, because the stories keep coming out too long. How can I "filter" the job, or extract short ideas and work?
I write a lot of tiny stories. There are no rules about what they can and can't do, but usually mine focus on a single moment. I include minimal descriptions and minimal dialog, when necessary. I usually write the event then add little bits of the surrounding story: why did it happen and what were the repercussions.
The best advice is probably to read a lot of them. Learn from other authors. Look for flash fiction and microfiction. Sherrie Flick and Lydia Davis write a lot of tiny stories and they do it very well.
First, direct world building and character building goes out. "Show, don't tell" becomes your first commandment and you dive right into story progression, establishing the world, characters and mood as a side-effects of the plot. A man in a spacesuit, riding on a camel through a desert is worthy two pages of traditional worldbuilding. Give him scars, a plasma gun and foul language and you have another page of world- and character-building done.
Cut down on full originality of the setting. Using generics - common tropes, common settings, character archetypes, allows you to squeeze into 2 lines what otherwise would take half a page. Apply quirks and modifications as you like, to provide the necessary originality, but you have no room to establish something entirely new from scratch - you obtain the effect by mixing generics. Generic history elements help building it.
Example: Instead of establishing from scratch a tribal culture with own traditions, mystic rituals, thriving on bloodlust, and menacing the population with raids, have offspring of an order of monks exiled from their monastery two centuries ago, turned nomadic rogues, seeking revenge on descendants of their enemy but cultivating traditions and rituals of ancestors.
Drop enough hints, and the reader will be able to build the whole world without need to establish it verbatim. You have the story to tell, and everything else happens as effects of flavors in which you write that story.