Plotters (that's me) love to plan, make lists of character traits, draw maps of where their stories are set and are in danger of never getting the story written.
Pansters need know nothing other than the starting point of their story. They live through the characters and are happy to let said characters rule the roost and lead the story.
Quite frankly, that scares the daylights out of me. Of course, nothing is life is ever just black or white.
Many writers find a happy medium by doing a little planning, but not to the enth degree, and letting the characters lead the way, but not so much that they lose sight of any meaningful plot.
My starting point is where I am so excited about the story idea that I can picture the main
characters. I am so emotional invested at this stage they I have to dive in to any scenes that come to the forefront of my imagination. To pause her and plot or list make would definitely stem the creative juices. Once I come to the end of that initial excitement and aren't sure where to go next, I find it helpful to sketch the bones on the story. To figure out where my characters are trying to get to and what is standing in their way. For this I need to do a little research and brainstorming.
No matter what method you use, it's important to write fluently until you have a first (rough) draft. So many people get waylaid and never finish. Even when you have a draft, you still have a long way to go, but all the gap-filling, grammar corrections, dialogue, layering of scenery, senses and emotion, is all just icing on the cake.
What's your process?