here is a useful tip, draw out the fretboard of the guitar, with the notes up to 12 fret on it, find out what makes up a chord[eg 135 of a major scale or do me so in tonic solfa] then you can see where you have all the different inversions of chords all over the fret board , right in front of your eyes,
then explain that the difference between a major or minor chord is the flattened [me third note of major scale], then show power dyads[2note chords doh soh] and explain that these are suitable for certain modal tunes.
reading music is not as essential as understanding what you are doing, if the instrumentalist understands what he is doing he can make quicker progress.
for example Banjoman, some appalachian tunes are in sawmill tuning dgcd, the way to accompany a lot of these tunes on the guitar, such as lady marget.. if it is in g modal, is to use E sus 4 EAB and d major, CAPOED ON THIRD FRET.
THE E SUS 4 or is neither major or minor, or to play an e power chord all e and b
now it is possible to stumble across this accidentally, but if a person is taught this he will probably discover it more quickly.
so understanding how to harmonise modes and knowing what you are doing is im portant for accompanying guitarists.