If you'd like to experiment with the literary form that is the drabble, my first advice to you is to not try to write a drabble. Taking an idea and drafting it in exactly 100 words is a highly restrictive task that compromises the fabric of the story you are trying to tell. The first step in crafting a drabble is to find an idea that you believe can terminate in 100 words. This may take some practice. If you aren't familiar with writing flash fiction, you may find yourself taking your story idea and turning it into something many times longer than a drabble. That's perfectly fine, if your goal is simply to write a story and to have fun doing so. Coming up with a drabble idea is quite difficult and not fully predictable.
The second step in crafting a drabble is to write a story based upon your idea. If you want to make an outline you can, but for something this small, an outline only compresses the freedom of your writing. It doesn't matter how long your first draft ends up, though any longer than 200 words and you'll have your work cut out for you.
After you have your first draft of your story, which probably isn't a drabble, but could be, the next step is to add or cut words until the story is within a few words of your goal of 100. So far as I remember, I've only actually finished a story in less than 100 words while attempting to craft a drabble on a single occasion. Normally, you will end up with more than 100 words and have to cut. For the rest of this post, I will use my story "One Test Remains" as an example.
I wrote "One Test Remains" at a musical practice one day, with a pencil in a notebook. It finished out at 124 words, not all that bad. The same notebook contains the first drafts to two of my other stories, "Once and For All" and "An Ancient Beverage." Those stories finished at 139 words and 127 words respectively. When I went to type up "One Test Remains," I tried to get it as close to 100 words with basic cuts as possible. (For "An Ancient Beverage," I actually rewrote the story to 106 words directly in my notebook.)
Here is what the first draft of "One Test Remains" looked like:
Phillip dropped to his knees. The iron head of a throwing ax arced over his skull, rending a patch of thin grey hair from his scalp.
“Good work,” Commander Jean said. He strode past Phillip and pulled his ax from the grass.
“Am I a sage yet?” Phillip asked. His wrinkled cheeks rippled.
Jean consulted a long sheet of oiled calfskin. “One test remains.”
“And that is?”
An ancient man, his skin dripping from bony limbs, hobbled onto the green from the barrack. A green orb was etched below his right eye.
“Him,” Jean said. He frowned. “You must kill the Elder in order to become a sage.”Phillip’s mouth went arid. “Father.” A sphere of blue flame erupted from his palm. “Forgive me.”
It's a pretty tight first draft. However, when you write a drabble, you have to cut everything that can be assumed and every adjective that doesn't matter to the story.
This is what the final draft looks like:
A throwing ax arced over Phillip’s skull, rending a patch of thin hair from his scalp.
“Good dodgery,” Commander Jean said. He strode to his ax.
Phillip’s weathered cheeks rippled. “Am I a sage yet?”
Jean consulted a sheet of oiled parchment. “One test remains.”
“And that is?”
An ancient man, skin dripping from bony limbs, hobbled onto the green from the barrack. An orb was etched below his right eye.
Jean frowned. “You must kill the Elder in order to become a sage.”Phillip’s mouth went arid. “Father.” A sphere of blue flame erupted from his palm. “Forgive me.”
As you can see, they're quite similar, the second one just has as few descriptive words as possible. You get all of the story and its associated flavor but almost nothing else. That's what drabbles are for. They allow you to infer a huge story through the reading of a microscopic story. Most adjectives can be deleted. An action can be replaced by a change in dialogue. Any word that isn't required by the story can be removed.
I don't have an intermediate step to show, but often when writing a drabble one round of editing won't get the story to exactly 100 words. In that case, give the story a second pass and really focus on exactly what the story is trying to do. Often, the essence of the story is at the very end, for drabbles. In this case, it's the reveal that to become a sage, Phillip must kill his father and that he is willing to do so. This implies a larger story, one set in a world in which patricide is not nearly as taboo as it is in ours. It also allows readers to wonder what sort of person Phillip is. The 84 words leading up to the final paragraph allow the final 16 words to have an impact.
Crafting drabbles isn't easy and crafting good drabbles is even harder. I've written about nineteen drabbles, three of which I expanded beyond 100 words (such as "Thought He Looked Familiar"). Of the sixteen stories that remain drabbles, I only consider nine of them to be good, as compared to my full pool of work. Three of them were published by SpeckLit.com, where I was paid the minimum professional rate of the time. If you'd like to read some drabbles before you attempt to craft them, I definitely recommend reading some of those to be found at SpeckLit.com.