How do you tackle a theme?

This last workshop has, in my mind, the great perk of variety. We read six stories with very different tones and styles and that made me wonder.

When I work on a story I tend to follow one of two approaches, either I tend to write the whole thing in a straight, linear and more or less chronological sequence, or I jut down a bunch of scenes that I know I want to see in it and try to find a way to connect them together. Both have served me pretty well, but I'd like to hear from other writers about what kind of approach they use to writing, to circumvent writing block and to avoid writing themselves in a corner or in the middle of everywhere (i.e. putting a character in a position where every possible action would result in a spawning a new storyline, rather than focussing on the main one).

Most of all, I want to understand how people like to work on themed story, who prefer to write an ad-hoc piece fitting the exact criteria and who loves to work with nail and file to hammer an existing story into shape.

For me writing occurs in three very different phases - imagining, recording, editing.

I'll get an idea for a plot, or character, or a piece of dialogue. Mostly I just need a somewhat distraction-free space to zone out and listen to my characters talk to each other, or work out a character background, or a plot framework. Sometimes reading, or looking at pictures puts an idea in motion. Once I have a tidbit, I'll turn it over in my head a few times, maybe polish it a bit... and if I don't immediately stop and write it down it'll just sit there hogging attention for a while and then finally dissipate into long term storage. I've learned that basically I think in snippets that become about 400 words long once they're written down.

The critical step for me is slapping it down on the page - poorly structured, warts and all. Get those 400 words worth of idea secured. Its the only way to really cleanse my palette. And if I'm lucky as I'm dumping to external memory, my brain's already moving on to the next part and I'll basically zip along writing down what I just thought of 15-90 seconds ago and the process sort of looks continuous. But its really still taking place as two separate activities, the thinking of it and the getting it onto the page.

Once it's on the page and I no longer have to try and hold the whole thing in my short term memory I can edit it. That's usually where the majority of the magic occurs. I can fix word choice, work on flow and sound, identify gaps (wait, Character A doesn't know that yet... need to go back and introduce the information earlier...), create or close loops of self-reference (putting ammo in Chekov's Gun ), and generally spruce the place up. My notebook thread is largely a motivational trick about putting stuff into the public eye while it's still relatively rough, forcing me to jump on it to clean it up fast before too many people see it in its slovenly state .

(By way of a practical example, while writing 15 minutes of Fame Ella didn't exist until coming to the end of the rough pass I though, 'dude, it'd be awesome if some of this energy Liam's tearing off Katie hit somebody...!' Ella was created at the moment of her uberfication, and then I went back through the story to first introduce her, and then to give her a handful of minor appearances just to keep her there in the reader's peripheral vision. Then boom: the payoff. But also about 8 more editing passes after that to polish the loops of foreshadowing and delivery.)

As to working with a theme, well, the imagination step is usually a bunch of processing inspirations - wouldn't she be greats as an uber?, what about a genie wish gone out of control?, I want to make a joke about Disney movies... Hey, do a story with power transfer, and a catch. On a good day the theme itself is inspiring. Like others have described, I usually know roughly where I'm going end up with a story, and I generally put in some brain sweat creating the starting point, but in the initial draft the route between the two can be shockingly linear with at best a twist or two I know I want at the outset. All the little scenes and beats that give the story it's feel rarely show up in my mind fully formed. They get worked in during edits. "There is no good writing, only good re-writing" So true, at least for me. And while I can re-write in my head, its just EASIER to do it externally. I am all about easy: it lets me get farther before I run out of mental energy.

I suspect Woodclaw mentioned 'hammering into shape' as he knew "15 minutes of Fame" was not my original story idea for the workshop. I had a different tale in mind with a fair degree of outlining done and a much MUCH more conventional power transfer story (the twist was funny though, so maybe I'll do more with it at some point). Alas I didn't find the essential need to make it happen. Fortunately another story I was already well into (and was rolling on like a freight train down a steep hill) almost coincidentally involved a transformative process that was fairly close to being power transfer (though a little peculiar by virtue of being 'crowdsourcing' rather than drawn from a single donor). So I reworked a few necessary introductions, tuned some of the steps along the way to make it more evident there was transfers occurring, and submitted it. (I'd have ranked it about 3rd-4th myself, at best a toss up against Touch and Go, but folks seemed to like it .)

Thank you all for the answers, some I already knew, some I didn't.
Still most of you only answered half the question, so I might reiterate it. All good for the technical pov, but I would like to ask about the gut part of writing a story.
We all have our little quirks, but when you think about a story, especially about defining characters, what is the pivot to build them around?
Make them believeable? Functional to the narrative? Or else?

Also, I'd like to put forward a couple of personal questions.
To Shadar, you mentioned the snowflake method, can you give us a bit more details.
To DKC and Ace, while I subscribe to the idea that it's a good idea to know where a story is going, how do you avoid writing youself in a corner? I have a hard time not to do it with open-ended scenes.