Some of the more useful technique books I have used are Aaron Shearer’s Slur Ornament and Reach Development, Ricardo Iznaola’s Kitharologus, Scott Tenants Pumping Nylon and Joseph Urshalmi’s A Conscious Approach to Guitar Technique. In addition, I would highly recommend Simon Powis’s Major and Minor Scales and Arpeggios for the Classical Guitar as well as his Technical Routines for Classical Guitar. These can be downloaded at classicalguitarcorner.com. Also, don't forget Abel Carlevaro’ Serie Dedactica. Finally, Jeffrey McFadden’s Book Fretboad Harmony, Common Practice Harmony on the Guitar is a must for all guitar students! There are many other fine pedagogical books and articles available. Seek them out! It’s a great time to be a guitarist.