This is what I do:
I usually just start with a raw feeling, or maybe a line or just a phrase. Most of this stuff comes from the way I feel when I’m writing, or characters take the form of a certain person I’m thinking about. Then I start to gather up the details in my mind – the setting, the situation, the characters. After that, I usually just write.
Most of the time, the first draft is way too long, and it kills me to pick off the little details in order to make the story fit the character limit.
After it’s all done, and short enough to publish, I come up with the title, then the tags. I usually have a hard time coming up with a title, for some reason.
I draw a LOT of inspiration from music. I’ve got a playlist of songs that, for some reason, just help me to write. And I can pretty much always come up with something when I’m listening to those songs.