This is what I’ve learned about writing: Make an outline before you begin a large project.
Here’s how you do it: Buy a huge artist’s drawing pad. The biggest you can find. Or a whiteboard.
Begin drawing a storyboard of the plot. Next, draw boxes for each major character and insert their characteristics. What they look like, how they dress, what they like to read. As much as you know about them at that moment.
Eventually the bones of the novel or the story you’re working on will appear. Of course, as I do, you can erase and change the storyboard as many times as you want. But it really helps to stay on track.