I'm a big fan of Chekhov's Gun. It's a useful for any type of writing:

"Remove everything that has no relevance to the story. If you say in the first chapter that there is a rifle hanging on the wall, in the second or third chapter it absolutely must go off. If it’s not going to be fired, it shouldn’t be hanging there." — Anton Chekhov

It's a reminder to keep the draft focused on its mission. It's easy to let yourself stray into side essays and random thoughts. I have to remind myself to have editorial discipline. I don't always succeed. But I try.