One of my favorite topics of course.
I've been focusing almost exclusively in the flash/micro fiction area for the last year+
Flash has to 'cut to the core' -- particularly the shorter the story (as in microfiction/drabbles(100 words - which I'm enthralled with at the moment).
Most or much flash seems to rely on a significant twist at the end that causes the reader to rethink, reexamine and likely re-read the story almost immediately.
Now certainly not all flash does that, but I think most of the best flash does.
It can also rely on a completely different perspective that is created and maintained throughout the story. One of my favorites in this respect is
The Stones by Richard Shelton.
Word choice is extremely important in flash, consistent interesting narration is important as well.
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