It's been 2 years since I did NaNo, so I'm little rusty at it, but I figured it's time to take it on again. For preptober, I just try to outline broadly. Mostly making sure that I know how the story is going to end, the main thematic elements, and any major character development.
Then I'll do a play by play for each chapter until November gets here. Basically list a summary of each event/conversation that happens in order in what will eventually become the body of the chapter. That really helps later on when I get stuck in the transitional moments.
The last thing I do is binge any playlists or inspiration boards I've made for the project. I think that's an important step that people don't necessarily see as "writing" but it's super helpful for me to stay in the space of the universe that I'm working so closely with.