For me, the key is set and setting. I go somewhere without other people, silence notifications, and start working while listening to light music or a familiar

For me, the key is set and setting. I go somewhere without other people, silence notifications, and start working while listening to light music or a familiar audiobook/podcast/etc. There's nothing magic about listening to things, but over the years I've avoided doing things other than creative or deep work while sitting alone in a room half-listening to something, and now when I do that my mind sort of takes the hint. Back in college, I saw a lot of people do this sort of thing to study. You'd see the same people at the same library tables week after week, friends didn't let friends study in bed because beds were mostly for sleeping, and there were always a few people who staggered unsteadily into exams to try the whole "state-dependent memory" thing. It wasn't particularly evidence-based, but after a few years of wildly oscillating between thinking about different topics, you notice that your brain likes to associate modes of thought with sensory input. I doubt my experience is unique there.