What I do personally is keep a simple Google Doc (which I call a Spark File) where I just write down ideas as soon as I get them, in the most pristine way, and

What I do personally is keep a simple Google Doc (which I call a Spark File) where I just write down ideas as soon as I get them, in the most pristine way, and then forget about them. Sometimes I get very interesting ideas, note them down, and after a while I come back to them and decide to build them. While I'm building I'll also note down any idea I get (be it related to the project I'm working on or something else) and just forget about it for the time being. Once I'm done with what I'm supposed to do, I'll open my Spark File again and scavenge for interesting ideas to either expand my project or start a new one.