An interesting video lesson by Bradford Werner

In this video, Bradford Werner talks about the right hand thumb position and the related exercises.

[embed]https://www.youtube.com/watch?v=BpU1zYKp404[/embed]

When adjusting your hand and thumb position remember to also consider your guitar position, footstool height, and all the other variables.

In the video Bradford also mentions a famous book, The Bible of Classical Guitar Technique by Hubert Käppel, a 246-page course book that contains many technique exercises (arpeggios, scale exercises, hammer-ons and pull-offs with the left hand, tremolo, flamenco techniques, speed training, vibrato techniques and dynamic exercises).

It can be easily found on Amazon.