Over the years I've refined the process, adopting the attitude of charging full speed ahead with the first draft, adding notes in places where the scene wasn't fully developed in my head in the interest of keeping the project moving
The problem is, I don't always think linearly, especially when it comes to series novels. Maybe it's because I know the endgame, but I tend to start looking at the whole project at once and certain parts just become more appealing to write. Sort of like having a buffet in front of you and heading for the desserts first.
When I first started doing web design, I would keep a pad by my computer to write down the font names and sizes and the hex codes of colors I used on the site. Unfortunately, you can't actually see a color code. It's just a series of characters. That's when I began creating palette images. At the beginning of every project, I would create an image with actual color swatches labeled with both the hex and RGB codes, as well as font samples and names. It was an invaluable resource, because instead of combing back through the code to find the color I used on this font or that background, all I had to do was open the image.
And that gave me an idea. I've been working on books 2 and 3 of the 'Ru Lexicon series (yes, both of them at once), mostly collecting scenes and putting them in a Scenes folder under the book title. I also keep a copy of Book 1 on my desk for easy historical reference (honestly, I have never been able to figure out how authors of multi-book series keeps everything straight). Normally, I pull the entire book together in a single draft copy, but that gets to be a pain when you're working on a scene halfway through the book and you have to go back and look up a minor character's name or where you first introduced a thread. Plus, because I write a lot of scenes out of sequence and throw them all in a single folder, I have to go back and find the point where I meant to insert it, and after a while it all turns into a big jumbled mess.
Which is how I came up with this new process. I actually got the idea from the way most movies are filmed. The director doesn't shoot the scenes in the order of the script. That comes later when the movie is edited together. So why not write a book that way? Instead of one big file of THE BOOK, have individual files of the chapters in that book, and "shoot" or, in this case, write them as the inspiration strikes. To keep all of this straight, I created a chapter summary document like my old web design palette, listing all the chapters with a summary of each scene in it, as well as the characters that are in that scene and the location of the action, sort of like a director's script.
Since I've started doing this, the book is coming together faster than ever before. I have files for each chapter in the book, and I populate them as I write the scenes, leaving notes in the places where I want to add other scenes. I admit, it's not for everyone, but it's a great tool for beating writer's block, since one of the biggest reasons a writer gets stuck in a book is because they don't know how to write the next scene or even what that scene should be. This way, you can just write other scenes and piece them together then fill out the transitions.