If you’re studying classical guitar the best method book I’ve come across (and the one I used) is Classic Guitar Technique by Aaron Shearer:
Here’s the rundown of the course books:
Classic Guitar Technique, Vols 1 and 2
Supplements 1 (Slur, Ornament and Reach Development Exercises) , 2 (Basic Elements of Music Theory for the Guitar) and 3 (Scale Pattern Studies for Guitar)
I still have my complete copies of these and still refer to them once in awhile.