When I started writing flash fiction, I assumed less was more. My max word count couldn't exceed 1,000 words, so I wrote a rough draft and then scrolled over my work, liberally tapping the delete key. I learned quickly and through the help of fantastic editors how to edit without sacrificing my story. It's common for writers to unintentionally remove important parts of their stories while trying to prune their work, but beware. Too much editing will leave your work with plot holes, character flaws and a jumble of confusion. Here's a few tips to avoid such a situation:
1. Don't sacrifice a good beginning. By the end of your first paragraph, your reader should be able to answer the 5 Ws. Who is the main character? What does he look like (I don't need to know he's wearing a red shirt, unless it's important, but it'd be nice to know a general age range so I can picture him while I read) and what drives him through the story? Where is the story taking place? When is the story set (historic, future, contemporary...a school, a bus, Mars...) Why is the main character doing what he's doing (inciting incident)? It's a lot, but without a good first paragraph, the reader will lose interest. If you don't paint the scene, the reader will be confused. If you don't set up the inciting incident, the reader won't connect with the main character or understand the point of continuing reading the piece.
2. Avoid cliches. This is something you should always do. In flash fiction, it's a good way to save on word count. Common cliches to avoid : you can't judge a book by its cover, the apple doesn't fall far from the tree, you can't please everyone, better safe than sorry, old habits die hard...
3. Avoid questions out of dialog. Usually when you have a question that isn't in dialog, the answer is obvious or already answered someplace else in the scene.
4. Don't sacrifice the basic story structure. Whether your story is 50,000 words or 1,000 words, it needs to contain core story elements and structure. Inciting incident, a quest or path the hero takes, disappointments, forks in the road for your hero to struggle over, climax, resolution.
5. End with resolution. Have the character learn something, or accept a difficult truth, or discover a crazy twist...just make sure the story has an actual ending, rather than feeling as if the piece stops because it's hit the max word count.
The best test of your fiction is to have someone else read through it and give honest appraisal. Start with these tips and keep at it. The rewards are worth the effort.