Writing flash fiction is not easy. So anyone who thinks they can just whip together a collection... think again.
I enjoy the writing process but in a different way from longer works. When putting together a novelette, it's several sessions of just nonstop writing. I set up the characters and the scenario and then it becomes a matter of putting as many words down as I can during my writing hours.
Flash fiction is not the same. It requires more brooding. More mulling. Let's be honest: the resulting story may only be twenty words long. So the words must be carefully chosen. A flash fiction writing hour may involve a lot of staring out the window then turning to the computer and spend fifteen seconds writing down those twenty words it took me an hour to think about.
It's kind of creatively draining. After putting together a flash collection I often find it a relief to switch to something longer. Something more "brainless" (bad choice of words, but you get it).
It's a good writing exercise, though. I would say the most important lesson I've learned from writing such short stories is how information is conveyed. Like most n00b authors my early stories are littered with a lot of dialogue tags.
"What do you have there?" she asked coyly.
"Why it's nothing more than a banana in my pocket," he said with a wink.
"Are you sure?" she laughed.
I still add the dialogue tags but not not nearly as much as I used to. It's a difficult lesson to learn because in order to take dialogue tags out you have to find a better way to convey the same emotion. Flash fiction lets you explore that concept. If your whole story is literally one conversation, everything about that conversation matters. It's not something that can be buried in a chapter somewhere while you hope that other conversations turn out to be more impressive.