Do you enjoy writing flash fiction, or like the idea of giving it a try? The definition varies--some people say flash ficiton has to be under 1000 words, some say 300 or under. There's even a version that is under ten words. There are no hard and fast rules about content or style or format, either, but the following tips might be helpful:
1: Don't try to tell the same kind of complete story you'd write in a novel. This sounds obvious, but a lot of people still try to cram in too much information. It's OK just to imply what happened in a part of the story you don't have space to tell. For instance, in a novel you might describe how your protagonist lost his job due to cutbacks. In a flash fiction story he might be drowning his sorrows in a bar and we pick up clues about what happened but it's not spelled out.
2: A good simile for some kinds of stories: flash fiction is like a snapshot. It captures a moment in time. We can deduce all kinds of things from it but we'll never know for sure whether we're right.
3: Be sparing with adjectives and adverbs (good advice for longer works, too, but especially important for very short pieces). Each descriptive word will stand out so make sure it's one that really says what you want it to.
4: Focus on one element to be the focus: character, setting, incident. You'll probably have all three, but decide which one is in the foreground.
5: A twist ending: not mandatory, but very effective if done well.
6: Leaving something open (as in, what happens after the story ends) can be a powerful way to make your readers think long after they finish reading.
Have fun!
(Tips galore and friendly guidance? You'll find them in "Your Writing Coach" published by Nicholas Brealey and available from Amazon or your other favorite bookseller.)