Here’s how it works: Imagine you wanted to play the note G several times in a row. You could simply hold the 8th fret of the second string and pick repeatedly [Ex. 1]. However, to make the resulting sound more interesting, you might consider using the guitar’s equivalent of a false fingering on every other note. In this case, that would be to alternate between the second-string G we just played and the identical (but different sounding) pitch at the 12th fret of the third string [Ex. 2].
Things get more fun when you employ false fingerings within a longer phrase. A repeating series of notes like this [Ex. 3] can build intensity, especially if you make it more rhythmically interesting [Ex. 4]. In this last example, I’ve taken the previous example’s four-note pattern and applied a triplet-sixteenths feel to it so that it repeats three times—with different rhythmic inflections—over the course of two beats. You can also jump around between different string sets and take advantage of multiple false fingerings within the same line [Ex. 5].
As I demonstrate this to you, though, I’m aware that I’m playing very—how do I put it?—guitaristically, and not particularly musically. This approach is much more powerful when it’s used in a tasteful and musical way. You don’t want to lean on devices such as this too much. Take inspiration from John Coltrane—he did this stuff all the time, but never let it get in the way of his soul.