Generally I will deconstruct their work by sitting down with some of the songs they've played and learning each section note for note. I will add here that I'm generally not a purist for N4N on stage but this is something I do for players whose work I revere because I feel like knowing what they did and figuring out how they did it makes me a better player. Chuck Rainey and John Paul Jones are both significant players for me, so I study their work in this way. I deconstructed the entire Aja album one year as an exercise and learned to play every song on there as close as possible to the original version.
One thing I learn when I do this is what my technical limitations are and, in pondering those, whether it's important enough for me to spend tons of time figuring out how to overcome those and, if so, what the learning process is for doing that. Rainey plays a lot of ghost notes, and I found out pretty quickly that I'd waste tons of time if I tried to incorporate all of that in as I went along. So learning his lines helped me refine my way of learning, in general. I learned the meat and potatoes of that stuff first, then I would go back and pick up some the smaller nuances, but maybe not all of them. This way of learning has served me very well in getting things stage-ready.
John Paul Jones presents a different set of limitations because he never plays the same thing twice and, on a technical level, he can be wicked fast. I can't play as fast as he can; just can't do it with the ever-present swelling in my joints, so I have had to learn that there are some places where I have to invent good compromises and other places where I just have to concede that it's above my pay grade. It's taught me to be inventive about overcoming some of my limits.
But, overall, what happens is that I add phrases and various things to my player's toolbox that I might not have thought of on my own.