For just jotting down ideas, a notebook, or I try to at least have a scrap piece of paper on me. I also ALWAYS have a pen on me. If I have no paper I will write

For just jotting down ideas, a notebook, or I try to at least have a scrap piece of paper on me. I also ALWAYS have a pen on me. If I have no paper I will write on my forearm. You don't need to write the whole idea usually (unless you're half-asleep, or in the shower, voice memos are better in those cases), you can usually just jot down two words to remind you later. I also use my phone, but typically for longer notes since it's a slow phone and takes forever to open the notes app. When I have access to the notebook, I'll write down my ideas properly the moment I can. If the ideas aren't important, I let the little pieces of paper accumulate until ~once a month, along with the notebook and the notes on my phone, I clean them and sort them into my computer. If you don't do this though, it becomes a pain, because it's often hard to decipher what the hell you meant by a note weeks later. Doing this also helps you form more connections/ideas from what you review usually. When I do this I also make sure to mark the idea as transferred since sometimes I might keep the papers or only transfer half (just the text when there's a drawing). As to where I put them, I used to use Evernote to manage everything but it wasn't working for me so I switched to Scrivener. Until now it's not working for me either (too many notes), and I haven't found anything that works so now I'm working on my own solution.