In On Writing, by Stephen King, he goes into great detail about his writing process.
The upshot is that he's what some writers call a "Discovery Writer", he sits down at a blank page with an image, or rough idea, and just writes and sees what happen. (George RR Martin/Game of Thrones is also, believe it or not, a discovery writer).
I'm not familiar with Asimov's process, but based on Agatha Christie's genre, I'd be surprised if she didn't structure hers fairly heavily.
The upshot is that he's what some writers call a "Discovery Writer", he sits down at a blank page with an image, or rough idea, and just writes and sees what happen. (George RR Martin/Game of Thrones is also, believe it or not, a discovery writer).
I'm not familiar with Asimov's process, but based on Agatha Christie's genre, I'd be surprised if she didn't structure hers fairly heavily.