Flash Fiction is typically short, 1000 words or less, and written quickly, over a few days. It's often done as a challenge to a prompt, such as a photo, a song, a mash-up of genres, or maybe a random selection of keywords. The point is to push you a bit, to get you out of a rut. In addition, for me anyway, it's not something to be revised over and over, it's just a quick way to try out a new character or situation or genre. You may end up with just a part of a story, a scene, a fragment—that's fine. I know that there are many sources online detailing how to perfect your craft, but I'd suggest you initially keep it simple and just write.
I used to be part of a site by the same name, here, and did 100 or so Flash Fiction then. Some were good, some were meh, and I occasionally found a recurring character or theme in several that suggested a novel. However, the organizers have not been able to post for a while. I still wanted to start doing this again. Hence this site.
I have a number of story ideas already, from various sites or just my brain, but suggestions are welcome. I'll post a new prompt here each Friday, with the FF due by the next Friday at noon EST. Post your story on your blog, with a link in the comments of the prompt post. Both comments on the stories and critiques are welcome, just be respectful. Start with what you liked, then suggest what could be improved, and maybe how you would do that. The point is for all of us to practice writing on a regular basis, try some new things, get feedback, and improve our work.
Note - you retain all rights to your work - just sayin'.