'Where do you get your stories?'
What a frightening question. A muse is a very unpredictable thing. You don't want to examine it too carefully in case it vanishes. I'll approach the question obliquely and hope my muse won't notice that it's being discussed.
Writing, whether in sublime inspiration or in dogged, deadline-driven desperation, is like holding a sword. If you grip it too tightly, you can't move fluidly and react quickly; if you hold it too loosely, it flies out of your grasp and beyond your control. I recently came across the terms 'planner' and 'pantser' to describe two types of writing: planning the story in advance or making it up as you go along (flying by the seat of your pants). I don't think any writer has to choose one way of writing or the other. In storycrafting, there's a time to plan and a time to fly.
The sword analogy works a bit better for me. Swordsmanship has its drills and set movements. You could choreograph a form that's very traditional, precise and beautiful. But the kind of movement you produce when you're responding to the challenges of an actual attack — that's something else altogether. It may be scrappy or rushed, but it has an energy and immediacy that's beautiful in its own right.
I have planned stories. I've planned how to tell them, what the characters should be like, where it should take place, what should happen, and how it should all end. Planning a story is a learned skill that requires you to understand the elements of story and how to manipulate them. It's good practice and it results in an excellent framework. It is, however, a mistake to hold onto the plan too tightly, because eventually there will come a point when the story will start to manipulate you.
Let it. Sometimes you can plan badly and not realise it until you begin the detailed work. Sometimes you plan quite well, but there's another movement — more efficient, more artistic — that will take the story where you want it to go. And sometimes there's an even better place to go that you can only see when you're in the middle of unfolding the plot.
There's a third 'P' to the formula. When you can't plan and the story won't fly, it might be best to pause.
Another name for a muse is flow, and flow can't be pinned down permanently or called up on demand. A nap, a moment's meditation, a prayer, a return to the rest position: these all serve to place the mind in a more flexible and receptive state. If the story is stuck, you need to find inspiration, and inspiration means that you take a moment to breathe in. Breathe out story, breathe in life, breathe out more story.
I know... very vague and mystical, but remember I can't be too direct lest my muse overhear and go wandering. I'll leave you with something more blunt and commonsensical, the best advice I know for swordfighting, writing, or living.
Don't undertrain, don't overthink, and don't forget to breathe.