Before you start to learn guitar scales, you need to make up your mind for being disciplined. Many people take the task to be an overwhelming endeavor. Though some self taught guitarists may consider this task to be unnecessary, you need to have a good understanding of scales, as well as modes to become a good player of the instrument.
Since scales are the foundation of melody and the basis of all chords, you won’t be able to go too far without having an understanding of them. Learning the guitar scales also offer your ears excellent training, which would serve you well in the long run.
A good starting point to learn your scales is to start with pentatonic and diatonic scales. Pentatonic scales have five pitches per octave, and are the first step for you to play rock solos and blues in future. The root and minor (flattened) third of the musical scale along with the fourth, minor seventh and fifth form the minor pentatonic, while the major pentatonic makes use of the second, third, fifth and sixth intervals apart from the root.
Diatonic scales are often considered to be extensions of the pentatonic patterns and consist of seven note groups. The diatonic scale forms meant for A, D and G would need a finger extension on your part, as they extend to more than four frets. Since you can use seven notes in diatonic patterns, you have a wider range of possible combinations as compared to the pentatonic scales that use only five notes.
When you learn scales on guitar, go slow. It’s better to learn a single scale at a time rather than going for all of them at a time, as the latter will overburden you. Try to use different positions on the neck while learning diatonic and pentatonic scales. Note the root of the scale and count the frets so that you are able to name the scale while practicing.
You can start playing the scales in CAGED series to understand how one pattern relates to the next. Begin with a slow tempo and increase it by 10 BPM by using a metronome or drum machine to help your practicing sessions bear fruit.