Interviewers often ask, "Are you a plotter or a pantser?" My answer would be, "It all depends. Usually, when an idea presents itself, I jot down a setting and some character names. Then I research the setting, especially the time period so as not to have any anachronisms floating around, and make notes. Then I jot down some ideas about the plot--where it's going and how it will get there. I might even fill in character descriptions and back stories.
But not always.
Sometimes I get an idea and just start writing, and when I come to the end, I really really like it or just want to hit 'delete'. I don't think there's a definitive answer about 'how' to write. I've read a lot of books on the subject and have come away with some good ideas, but even then the ideas have to be adapted for me personally.
A short story can just sort of 'go', where a longer novel needs a few guidelines so it doesn't become too convoluted. Also, what works for one author doesn't necessarily work for another.
I spoke to a group about the Penelope series, and immediately someone said, "You do have a murder in the first chapter, don't you?" When I replied in the negative, she became adamant--"You have to follow the rules." Okay, honey, you follow the rules if that's what floats your boat. I write for myself. And, btw, the number of books sold in the series indicates that readers haven't heard about 'the rules' I didn't follow!
It's been great to have a series which has sold well, and maybe it will happen again. Or maybe it won't.
The one thing I can count on is that I'll enjoy what I'm doing however I do it. At the end of the day, that's what matters.