THe process is essentially one of articulating a vision. What you envision is wildly subjective. How you go about writing it? One way is to conceive of a tale, or a plurality of tales that will capture the vision, and then create stages for thoser tales, like story-boards. You can use index cards.

Then, the hard part, actually writing each one, shuffling the sequence, staying true to the characters, seeing the details.

The even harder part, rewriting, cutting out half your words, regenerating material to meet some better idea, rewriting again, rinse and repeat.

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