I have two main strategies for coming up with ideas:
The first is just start writing things down. It can be a list, a rambling paragraph, or whatever. It stems from advice I got from a playwriting professor who encouraged students to “write the bad play first.” This essentially means start writing without worrying about nuance or subtly or elegance - just get words on a page. Then as you swift through those words you’re likely to discover nuggets of ideas that can be extrapolated on and refined.
The second strategy is that I schedule a couple of half-hour walks every week to just let my mind wander (it’s important to no listen to music or podcasts or anything else during this time).