The best way to learn guitar scales is to study the relationship between notes and memorize their places on the fretboard. Beginning guitar players should use major and minor diatonic scales the most at first, but they should practice pentatonic scales as they become more advanced.
A major diatonic scale increases by two half-steps, which are equivalent to one fret on the guitar, per note. For example, a C scale goes C, D, E, F, G, A, B and the octave of C. The jump from E to F and from B to C is one half-step. The fifth fret on each string corresponds to the next string played open. Fifth-fret E, for example, corresponds to A, which in turn goes to D and then G. G's fourth fret is the open B string.
When playing a scale, it is best to let one finger operate a fret and only move when the whole hand has to move. Players should think of the major scale in terms of the fingers used to fret the notes: middle, small, index, middle, small, index, ring and small. This sequence holds no matter where on the fretboard the scale starts. When moving from the G to the B string, the player shifts up a fret. The natural minor scale uses the sequence: index, ring, small, index, ring, small, ring and small. Players should practice the scales slowly before attempting to build up speed.