As a practical matter, slipping from editing my second novel to writing the first draft of my third novel actually works pretty well.
I had been away from the third book for almost a month, and when I went back, what I found were pages of fat. Stuff I sort of liked, dialogue that had a nice flow to it, but which I could erase without hurting the story.
If I write first-draft material on a Monday and look at it on Tuesday, I’m often too close to see the problems. If I write first-draft material in November and get back to it in January, I have fresh eyes. I can see fat for fat. I can edit ruthlessly.
Novelist Joshilyn Jackson (creator of the Best Lead Paragraphs … Ever!) called the writing of first drafts “knitting bones from air.” She’s right. But sometimes, the bones we knit are un-opposable thumbs. You need time and space to realize: You gotta unknit that shit.