Most Common Chord Progressions on the GCF Accordion
As folk music styles, both Norteno and TexMex tend to be simple musics, employing a basic I IV V approach. Consider the following chart which shows the scale degrees for several keys.  The fundamental tone of the key, also called the TONIC, is represented under the column I (Roman Numeral 1):
I
II
III
IV
V
VI
VII
I
C
D
E
F
G
A
B
C
D
E
F#
G
A
B
C#
D
Eb
F
G
Ab
Bb
C
D
Eb
E
F#
G#
A
B
C#
D#
E
F
G
A
Bb
C
D
E
F
G
A
B
C
D
E
F#
G
A
B
C#
D
E
F#
G#
A
Bb
C
D
Eb
F
G
A
Bb
B
C#
D#
E
F#
G#
A#
B
:
The easiest and fullest minor chords on the 3-row Bohemian box are the IIm chords (minor chord founded on the 2nd scale degree), with the VIm chords (founded on the 6th scale degree) coming in as second easiest. Finally, the IIIm chord (founded on the 3rd scale degree) is favored in quite a few folk songs.
Thus, the most common chords in folk music for a given key are: I  IV  V  II  IIm  VIm  IIIm:
I
IV
V
II
IIm
IVm
IIIm
C
F
G
D
Dm
Am
Em
F
Bb
C
G
Gm
Dm
Am
G
C
D
A
Am
Em
Bm