Heres how it evolved for me...I would put on a blues album, figure out the key by sliding a bar chord around, then start playing the minor pentatonic scale, then quite haphazardly I would land on the same note as the artist, usually on a little descending lick that goes right down the scale, I would freak out that I just played the same thing as Hendrix or Clapton, and take note of where in that song that little lick was and then every time that part of the song would come around, I'd play that little "lick". Even though that "lick" was really just four or five notes in a row straight down the scale. Then while I was playing the scale I would notice that the root sounded just right at the end of phrases so I would make sure to land on the root at the right times. Then I learned a "turnaround" lick, and a little intro lick and you got it. Kinda. Its hard for me to learn from sheets or tab so I would just meeander around taking note where the changes were so I could be on the root. Its great to have some stock licks but stock licks become stale fast. Each song usually has a signature lick so you have to learn that. But you can be anywhere in that scale at almost any time and its probably right as long as you get that root at the right time. Blues is great because you can use those repeating licks to death and its still cool. Then add feeling and ....
I learned over the "John Mayall Bluesbreakers with Eric Clapton" "Beano" album. Theres also a lot of blues backing tracks that are just basic blues rhythms that will let you go anywhere.
