First of all, what is "Preparation for 3rds?"
This is when, for example, in the key of G, the progression
is going to the C chord. The chord progressions that play under the melody is as important as the melody that you want
if you don't understand the progression that is playing, you probably won't be able to create a decent melody
to play over those chords.
So the movement is from G to C.
It is very common, (and is a basic rule of harmony)
can always play the dominant 7th of any chord before
you go to that chord.
So the new progression would become G /
G7 / C.
So what is the difference between G and G7th?
An F note.
The following list are typical runs, licks,
adornos (whatever you
want to call them) that work really well and are very standard in
this style of Conjunto, Tejano,
Norteño. Try them out and see if
they sound familiar to you. I think that it would be difficult to
out by ear, but once you know them, they are invaluable runs for the style. Some of them can only be played in one octave,
others can be moved up an octave.
Preparation for 3rds.
Key of G
F3C6, G5, C346
Key of F
C4G6, G4, F3C17
Key or C
G34, C2, F345
Key of D
C3G5, (G1), G346
Key of Bb
F4C7, G6, C18
That's it. By the way, it is called Preparation for 3rds because
the Chords (in Spanish) would be G
= first, D = second, C = third.