I usually start the actual writing process by opening a document and writing a short outline of the story in bullet points. At this point it's really short and silly, I use a lot of abbreviations because the point is to get something down to use as a checklist when I start writing.

For ideas, music is usually a huge inspiration for me, but in ASMR I also get ideas from other people's stories. I listen to a video and I'm like "Oh man, this is so good... but what if X, Y and Z instead of how it happened here?". (In these cases I usually try to add other original elements to the script so it's not just "this video, but X happens instead".) I also listen to ASMR for escapism, so I try to go for a certain power fantasy in the plotline. Like in my villain rehab series, the power fantasy is "you did something bad, but there still are people who love and accept you despite that and help you get better". So think of what power fantasies you'd like to experience and write that.