I use my own system dubbed NL0 (N = Now, L = Later, 0 = Never). I keep a Trello board online with these 3 columns, and once in a while I clean it up (maybe once every month, but it's not a rule - whenever I feel like it). I also write things and ideas on paper, but, eventually, I sync it all up in the Trello board (I also have Trello on my phone, so, it's usually around when I need it). The [Now] column is for things I need to do / learn now (highest priority); the [Later] column is for things that I need or would like to do / learn later, in the medium-term future; the [0 (never)] column is for things that I am sure I won't do / need, or things that represent no meaningful value (for me) anymore, including things from the other 2 columns. It's been working for me for years now.

P.S.: I keep talking about things that you need to "learn" / "do". Actually that sums up everything we do in our lives. We either learn something or we use what we already learned. Keep learning, keep doing!

NL0 4ever! :)