The visual novel I’ve excerpted for Spring Thing started out as a short story (I considered myself a writer long before I considered myself a creator of any sort of software). That, in my head, is the “canon path” through (though not necessarily the only, best or worst).
Next (well, after a diversion where I tried and failed to get it illustrated, and concluded this might work better as interactive fiction), I looked at it and decided on the most important themes and ideas I wanted to focus upon.
At this point, I split the IF into sections, because as a novice IF creator, I know I can’t expect to succeed if I try to do the whole thing in one lump. Making a minimally-viable game, and then iterating based on feedback, makes far more sense in my situation. I initially split it into five sections (two of which run in parallel), but later discovered I needed to split the first “arc” into two to get a minimally-viable game that was actually “minimally-viable” (the minimum unit of narrative fiction is the arc, and I spotted that my first section had two small arcs).
Since I’m a new IF creator, authoring-system “shopping”, and learning the basics of the system, followed.
Once I had a section, I looked at it and decided where the challenge points were, and how I’d express that. (This was also where I decided to go for a puzzleless, choice-led mechanic for the section. I could as easily have puzzles in a different section, if there was a situation there that made sense for them).
Next, I wrote the writing and logic. I preferred to do these at the same time, and I mostly did them sequentially. Sections where I did not necessarily intend to fill sequentially were commented with a special tag, so I remembered to fill them all in later. Only once that was done and tested did I start the next pass.
Each type of multimedia got its own pass. Playtesting started before I did the music one, though (and continues, even though the excerpt currently in playtest has been submitted to Spring Thing’s Back Garden).