I can play guitar by ear (within reason - it's much easier for idioms I'm familiar with, and I don't have perfect pitch, so I need a quick exploration to find t

I can play guitar by ear (within reason - it's much easier for idioms I'm familiar with, and I don't have perfect pitch, so I need a quick exploration to find the key first). I had some guitar lessons as a teenager, covering a mix of technique, vocabulary and theory. But I was not academically schooled in music. There are two things that help develop this skill I think, extrapolating from my own experience: One is, when learning a piece I find it useful to hum or sing the notes I am trying to learn. i.e. play back a bit of the recording, then pause and hum it to myself while finding the notes on the instrument. It sounds trivial and obvious, but it helps build the connections and to hear the music in your head. I think part of being able to do it involves "having the instrument in your head". The second tip is then to follow on from the first but do it without a recording and without the instrument in your hands. Hum the notes to yourself and try to imagine where they are on the "instrument in your head". If you don't already know the key just choose an arbitrary one. This helps two things - develop the instrument in your head, also a sense of relative pitch (intervals) between the individual notes in sequence, and also between each note and the key centre. I distinctly remember as a teenager this was something I liked to do while on my way to and from school - hearing back a guitar solo in my head and trying to play it, in my head. And then when I got home I could try it out on the instrument and see how close I was.