I take them down either in my notes app or in my sketch pad.

If it’s by hand I’ll either toss it in with no sequential order or category, just a date at the top. If it’s something I important I’ll throw it on a sticky note. I do have dedicated notebooks for certain topics, I just transfer these notes to those if they’re significant.

In the notes app I have different folders of subjects like investing, sciences, musical inspirations, weird thoughts I have when I’m high, etc. and a massive note of stuff in general.

It’s a good practice to get into if you have trouble remembering things or want to scribble something down to come back to it later.