That's a great topic!
In my case:
In this jam i worked with my 3-piece music band.
Evening after theme reveal we started brainstorming story and plot ideas. Next morning after theme reveal we set ourselves 3-5 minute timers for like 10 times. Every 5 minutes you should come up with musical idea. Chords/melody/whatever. We worked on this separately. After few hours we came up with a lot of music ideas. Almost every one of them was little piano part 15-30 seconds. Then we gave each idea description like what emotions we feel about this sketch, what it can tells us. And those descriptions also helped us to build fuller story.
Next step - we organised our sketches in order according to plot and emotions. And when it's done - i started to expand them, with emotions and dynamic, that current scene is needed. Also in that step i started create sound palette that is common for all of the tracks. I came up with few leitmotifs, and in that step started to add melodies from one track to others, that share some common parts of a journey. Some of them share melodies, other - arpeggios and chords.
Next step - we recorded vocals and Voice for songs that needed them. Then looong couple days of arranging all of the tracks.
And... It's done. Dark story about one more journey :)
ENTIOX is waiting for you, stranger...