As mentioned previously, verbs are the most important part of any story because they are literally where the action is. And with flash fiction, this becomes even more important.
One of the things that makes weak writing is using too many weak verbs. Using "Raced" or "Skipped" or "Marched" in the place of "Walked" depending on the need of the story will amp the action up a notch, add understanding to the emotion of the story, and keep a readers attention. Why did the character race? Was he scared, the situation urgent? Why did the character skip? Was she happy, a child, stupidly oblivious to her dangerous situation?
Power verbs are always best. Finding new ways of saying things make the writing interesting. Unusual verbs are great if not over used.
When I was in a critique group, one of the gals used the word "Riveted" which was awesome the first time. But when she used it a second time in the same chapter, I encouraged her to find a new word for one of the instances. She didn't like the suggestion, but eventually went with it because such a powerful and unusual verb used more than one in a chapter, or even two within several chapters of each other, that powerful verb sticks out. That sort of verb would also stick out if used more than once in a flash fiction piece.
Use power verbs liberally. Use variety. Be careful about repeating the most powerful verbs, especially in short pieces, like flash fiction.
And for a list of power verbs you can look at the page I have started as a storage facility for power verbs I come across. If you have any to add to the list, I'd love to have them.