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.
The ways I discuss are: Destination Points; Groups of Two and Three; Rhythmic Variation; Articulations, Dynamics, Timbre; Tremolando Scales.
The ideas should be applied to all your scales and exercises. Each variation or idea will increase the difficulty of some aspect of the scale and should expose weaknesses in your technique that need to be addressed. Practice with all right hand fingerings: i-m, m-a, i-a, a-m-i, and use rest stroke and free stroke. Some examples are notated ascending only but continue the pattern descending as well.