IMO the best way for guitarists to learn to improvise is to study the work of the great improvisers by transcribing their solos and analyzing them as they relate to the chord progression and structure of the song.
If you are driven to learn and memorize a solo note for note, I fully encourage you to do so. I have done plenty of that in my life. But it can also be useful, and much less time-consuming, to look through a transcription as you listen to the track, get the gist of where the ideas are coming from (what scale/mode etc. is being used, where on the fretboard it is played, etc.), and single out certain passages that you may want to take a closer look at. Feel free to use these transcriptions however you see fit.
I am slowly building a collection of transcriptions here at HCG, so keep an eye on this page for new additions. Feel free to reach out to me if you have ideas for great solos to transcribe. Here’s a list of what is available so far.
Solo by Trey Anastasio on the Phish album Rift.
“Fire on the Mountain”
Solo by Jerry Garcia on the Grateful Dead album Dead Set.
“Touch of Grey”
Solo by Jerry Garcia on the Grateful Dead album In the Dark.
“Sweet Little Angel”
Solo by B.B. King on his album Live at the Regal.