(from the chapter on "Elements of Improvisation and Variation" in The Complete Dobro Player)
Though it technically takes a minimum of three notes to make a chord, dyads can be an effective addition to a rhythm section that already has a primary chording instrument like guitar. (The dyad can also be used in soloing.) So learning the two string patterns listed in Table II (in The Complete Dobro Player) and listening to how they sound over different chords can prepare you to think chordally. You might make a tape of yourself strumming the chords of a tune you wish to learn to improvise on. Then fool around with different two note combinations. Eventually you will be able to hear how a couple of notes will sound over a certain chord before you play it. Your ear's musical education is then well begun.

Think up two string combinations that move minimally while the chords change. This sort of suave voice leading can make you the idol of your peers. For example, instead of:

you might try:

The S1-F7/S2-F6 in the second measure of #62a is part of a G9 chord.
Analyze the scale steps.

The following typical circle of fourths (A7 to D7 to G7 to C progresses by going up a fourth interval) is a fertile setting for nicely connected dyads.

Example #63e is worth a closer look. As we travel up the circle of fourths playing dominant chords (major triads plus the b7) we can move this 1-fret reverse slant position chromatically downwards. Analyzing the scale steps in each chord reveals that with each move down a fret the steps invert from 3/b7 to b7/3 and back again. This kind of discovery seems to imply that there are other interconnections in music that might be found with such analyses (and there are). There can be a sense of true accomplishment when you start to hear and understand these relationships.