ok so let's say you have a big idea and it's kicking around in your head and it's really bugging you but you can't do it right now because of lack of skills/current commitments/etc. how do you write it down so that you know in the future when you come back to it arbitrarily in the future you know it will appear as vividly in your head as it is right now
write down all the details you know, and then get yourself on an audio recording talking about it and explaining (or singing/performing, if necessary) all the details you know. if that's not enough, do it on a video recording. if you can imagine it now, you can describe it well enough to revive those imaginations