What's your process for planning a story? Do you know what will happen in the beginning, middle, and end of the story before you start writing it? How about in each chapter? Do you do any kind of outlining or just fly by the seat of your pants? If you do outline, what does that look like for you? Do you ever write scenes in advance or visualize them in your mind? Do you change your mind often, or do you usually stick to your plans? Does the way you plan vary from story to story? Lots of questions, but they all go together - just describe your process!
I usually start with a situation that's going to be the basis of the whole story and work my way out from there. I figure out how my characters will get into that situation (the beginning) and where it will lead them (the middle), and how it will turn out (the end). I won't start writing without a beginning, and I usually know pretty early on how the story's going to end. The middle I tend to make up more as I go, leaving myself room to be flexible and change my mind. I just need to have a clear idea of where it's all going before I get too far into it.
I don't start a new chapter without knowing what it will be about, but I also don't plan out chapters in a beginning/middle/end way. I just start writing with a goal in mind of what I want to happen in the chapter and let it pan out however it pans out. Sometimes it turns out a lot different from what I had in mind, but that's okay.
As far as the overall story goes, I am definitely an outliner. I don't outline one-shots, but I have had some kind of outline for every novel I've written since You'll Never Walk Alone back in 2002. My outlines take different forms depending on the story and whether or not I have co-writers, but for my individual stories, they are usually more like timelines. I list the major events of the story in the order they happen and keep track of WHEN they happen. I can always tell you when my stories are taking place, sometimes right down to the specific date, other times just the month. I started doing it this way with Broken and have found it helpful mainly for my medical dramas (which would be a lot of my stories LOL). The only stories I've actually outlined chapter by chapter or scene by scene are Secrets of the Heart and some of my collaborations (Song for the Undead, 00Carter, Code Blue). My outlines typically also include information on my characters to help me stay consistent and sometimes bits of research that I want to remember to help me in my planning. Some of them get pretty long; my BMS outline has 24 pages LOL.
I do a lot of visualizing of scenes in my mind, but I rarely, if ever, actually write them in advance. Once in awhile I will type up good lines in my outline if I want to remember them, but that's about as far as I go. I prefer to write the story in order so that I can make sure all the scenes flow together. If I write a scene from the middle before I've written all the scenes leading up to it, I'm worried it won't fit by the time I work my way up to it, and although I enjoy editing, I hate making major revisions.
Sometimes I do change my mind about small things, but I usually don't stray too far from my original idea, especially when it comes to the major events of the story. The exception would be if I realize something I originally wanted to do won't work and have to rework the idea... and that is when writer's block tends to kick in for me. That's why I find it helpful to make an outline early on in the writing process so I can see the major events of the story laid out in order and make sure they all fit together in a way that makes sense.