This is from my new book Classical Guitar Technique: Essential Exercises, Scales, and Arpeggios. The 122 page book includes: Practice Routines, Tips, 100 Open String Exercises, 120 Giuliani Arpeggios, Scales, Slur Exercises, Shifts, Finger Independence, Barre, Tremolo, Common Harmonics, and much more.
Before proceeding to moveable scales that involve shifts, take some time to solidify shifts in the smaller exercises below. More shift practice can be found in scales, especially scales with open string shifts to high positions. Keep your fingers aligned (knuckles parallel with the strings). The arm moves the hand, do not outstretch the fingers or allow the thumb to drag behind when changing positions.
Guide Fingers – Guide fingers allow for greater accuracy when shifting and should be used whenever possible in repertoire. Keep the guide finger on the string the entire time. Relax your grip on the string but do not stop touching it. Try these exercises on all six strings and reduce string squeak on the bass strings by relaxing your grip on the guide finger (it will still make some sound but try to reduce).
Larger Shifts and Reducing String Squeak – Use your 1st and 4th fingers as guide fingers. Try the exercise in two ways: 1) Relax your grip on the string when changing positions but do not stop touching it (you’ll get a mild squeak). 2) Release your finger from the string completely but keep it extremely close to the string as a visual guide (no string squeak at all). Keep your left hand knuckles parallel with the strings at all times. I’ve notated the exercise on the sixth string but play it on all six strings.