The present letter is a very long one, simply because I had no leisure to make it shorter. ~ Blaise Pascal
Sure, he was referring to a mathematical equation, but it exemplifies my take on writing Shorts (and synopses too, but that's a different tangent). Unlike Jeffe and James, I find writing fiction under 100,000 words an anathema. I'm the chick whose first-drafts clock in at 250k or higher.
What? I like my characters to live robust lives.
The fact that I can get the second-drafts down to half of the initial word-count is testament to my cutting skills. Cutting isn't the way to write short. Trust me, I've tried. It doesn't work well at all. Novellas (20k-50k) will forever remain beyond me. Sorry, no advice on that front.
I have forced myself to write Short-Shorts, which are 1500 words or less. The only way I can write those is by repeating to myself one mantra:
Write the moment
A moment is all the word-count available. Every sentence serves the purpose of moving the moment forward. Short-Shorts are great writing exercises. There is no room for verbosity, but there has to be space for a story -- goal, motivation, conflict, and emotional investment. It's roughly half of a scene, so it is possible.
So, if you want to write short-short, put on your blinders. Write the moment.