I find scenes/ideas just sort of pop into my head, particularly when I'm working in a world and have future books planned in it. I tend to grab a sheet of scratch paper or have a file for that potential future book and just type them down with no formatting just to get them out of my head. 1) I don't want to lose them and unfortunately, sometimes even sleeping on it means I can't quite recall how I was going to write that scene out before. 2) It clears space in my head to relax and work on what I was trying to focus on and 3) When it does come time to potentially work on a sequel or short story, I've already got some material on hand.
Also, I tend to work on multiple works at once. I might be editing one and working on a first draft of another. Sometimes I can get stuck with things like trying to come up with chapter openings or certain scenes, so rather than sit there feeling frustrated when something just isn't happening right then, sometimes it's useful for me to be able to switch projects and give my subconscious the space to think on it for a little while.
Anyway, that's what works for me.