The advice I am giving always to all my students is above all to study the music profoundly... music is like the ocean, and the instruments are little or bigger islands, very beautiful for the flowers and trees.
When I started to play with my fingernails, it was not just for volume. The most important thing was giving the guitar different colors in its voices...
The piano is a monster that screams when you touch its teeth.
The guitar is a small orchestra. It is polyphonic. Every string is a different color, a different voice.
When one puts up a building one makes an elaborate scaffold to get everything into its proper place. But when one takes the scaffold down, the building must stand by itself with no trace of the means by which it was erected. That is how a musician should work.