Writer, director, and actor Taika Waititi shared his writing process during a BAFTA Lecture:

I do lots of notes and beats, and I try to figure out the story before typing because I find that typing is really horrible. It just hurts your body and your mind. I like to just have the whole plan out in front of me.

Basically I’ll start with the beginning and the end, something that I really like visually or I think “This would be a cool way to end a movie and that would be a cool last image for an audience to see, and this would be a cool first image and a cool way to open a movie.”

And then I’ll put in some scenes throughout that I think would be a great fit, and then eventually when I’ve got enough of these scenes or sequences, then, lazily, just glue them all together with some sort of connecting scenes.

But that’s it really, and when I know what it is, then I can write really fast.