Hello dear Maribel!
A few years ago I have been using Cuatristas.com and well, I am finally using it in the way recommended by you (Basic Level.)
Emepezé with the warm-ups and the exercises of the scale in DO Mayor. The subject I am practicing is the aguinaldo isabelino.
I sent my progress with this song. I would love to continue learning what I can improve about my general technique.