When I started to play guitar, I had a work friend who'd been playing longer than me and who had, consequently, advice to give. This was about 1964. He was a great exponent of something that had emerged around 1960 called "psycho-cybernetics". I've never known much about it, but he used to mentally 'play' the guitar in his mind - visualise his hands playing guitar pieces - close his eyes and play a whole piece as though he was seeing it before him.

Nothing clever about that, but I've also done this regularly when learning a new piece, particularly single melody lines on violin or mandolin or tenor guitar, and I have to say it's very useful indeed. I also do the same with the music - close my eyes or physically unfocus, and I can 'see' the music/words on the paper in front of me.

Doesn't stop me from forgetting things every time, though...!