I enjoy doing conversations with my past or future self.
What would past-me think if they could see what I'm up to right now -- what would surprise, delight, or disappoint them? How do I justify those decisions, and do those justifications stand up to their scrutiny?
What will future-me wish that I'd considered about decisions that I'm currently making? Is there anything about the present that they would ask me to do differently?
Of course they're both just mental models or shoulder advisors, but they're still mostly alright to talk to -- and if they aren't, if I'm being or becoming someone whose company I wouldn't want to keep, that's a useful signal in itself.
One prompt that often helps put things in perspective, though it's more of a thought experiment than a writing exercise for me personally, is to show my mental model of my distant ancestors around in my everyday life. Trying to figure out how I would explain mundane things to them often shows me aspects of those things which I had not considered before.