Such an interesting thread as someone who has taught for almost 3 decades.

Different people need different things. Some only seem to learn by doing, I however get a lot from visualisation (imagining playing something).

If I have a score and a backing track, then I start by following the score to the backing track (slowed down using the likes of Capo if required) before I even think about playing it. I'll admit now, despite the many sessions under my belt, sight reading is not my strength, it doesn't come around often enough. I visualise what I am going to do before playing, rather than 'jumping in blind' and feeling more frustrated.

Making sure you know how to accomplish all the pieces (any trickier chord changes/passages) before trying to put it together (i.e. breaking it down) is usually important for more challenging pieces. Some pieces you know all the 'bits' before, its more of a case of remembering which order to put them in.

I listen to music I'm working on while driving to and from the school I work at, so when I'm playing it's easier to put it together.

I don't only work on one piece - I need a switch up during practice time to keep things fresh so I don't get to dislike anything. If I'm working on a few jazz tunes for example, I'll spend a given amount of time on each, chopping and changing, giving more time to the one I feel I'm getting the least success with. I use either BIAB or iReal Pro for jazz backing if I don't want to use a specific released version to play to.

Do things that keep you enjoying it, don't punish yourself with it.

Best,
Karn@SussexGuitar