Eric Johnson used to write a column called “Wild Stringdom” for Guitar World magazine. I saw a recent post on his forums linking to an archive of one of Johnson’s old articles, in which he discusses his approach to soloing and shifting positions.
I always want to squeeze the optimum tone out of each note. Guitarists often say that your sound comes from your technique, your guitar or your rig. That’s true to a certain degree, but in my opinion, the finger you fret with and the string you use will also drastically affect your tone. I like all the notes in my lines to have a certain cohesiveness of texture. To that extent, I constantly work out my fingerings, using any and all permutations I can to play my lines. If necessary, I will skip around the strings in order for a passage to maintain tonal consistency; that’s why I might make some fingering choices that seem odd, illogical or simply more difficult to the average guitarist.
The article provides some insight into Johnson’s approach to fret fingering with some nice examples.