What techniques do you have to strengthen the inner ear?

Do you practice this? I have had some stints of meditation where I can hear music moderately well in my head, but I would like to get better at it. I would like the imagined sound to become more “real” or clear in my head. Some things I like to do are to imagine “pure” sound like the sound of a certain instrument playing a single note, or nature sounds like wind or water, or a certain piece as far as I can remember with timing included. For the last one, sometimes the timing might be hazy, like my head jumps to a next measure or passage, and then I am weirdly hearing multiple sections at the same time. If you have anything to share I would love to hear it.

Aside from the auditory imagination, I can also visually picture the keyboard in my head to play something attached to the sound, or I can also imagine the tones in relation to each other on a blank space kind of like midi notes.

I am also interested in creative ways to do this, like imagining sound that is not a song already, kind of like improvisation. What state of mind do you get in to be able to do this more?