If I just described your process of practicing guitar scales, don't worry, you are not alone. I have done the same thing for years and so have other guitar players, particularly those who are/were self-taught.
The good news is that there is a superior way to learn scales on guitar that will enable you to make more progress in less time. The single most critical point you need to remember is that it is necessary to fully explore every creative option offered by a new scale before you move on to start learning more scales. By doing this, you will improve your guitar playing with scales much more quickly and will enjoy the process of practicing guitar a lot more. Below I will outline for you several essential tips that will help you to get much more out of every scale you practice on guitar. Following this advice will enable you to not end up in the very common dilemma described above, and instead move forward much more quickly towards your guitar playing goals.
To see a more detailed explanation of how to use the points of advice described in this article, watch this free video lesson on guitar scales.
1. Get Specific About Your Scale NeedsDepending on the style of music you play, there will be some scales that are much more common to your guitar playing style than others (for example: the harmonic minor scale is much more common in neo-classical metal guitar compared to the blues scale, and vice versa for blues/classic rock guitar players). With this in mind, you need to prioritize your guitar practice time by focusing your attention first on getting the maximum creative potential out of the most important scales for your style. Only "after" doing that does it make sense to spend significant time to begin practicing exotic and unusual scales.
There is nothing wrong with knowing how to play lots of scales, but in order to truly get results from doing that, several things need to happen first: you need to have already done the work of mastering the most essential scales for your musical style (as described above), and you must have a reliable method for practicing that you can apply to quickly learn any scale on guitar.
You can use one of 2 ways (or preferably both) to achieve the goal above: you can either ask a guitar teacher to simply tell you what the most important scales for your musical style are, or you can improve your aural skills (ear training) and knowledge of how music works to hear what scales are used in your favorite music yourself.
2. Learn Each Scale All Across the Guitar NeckIf there is one mistake that most guitar players make over and over when learning new scales on guitar, that would have to be learning each scale in only one position on the fretboard. A fairly typical illustration of this occurs with classic rock guitar players who, after learning the foundational A minor pentatonic scale on the 5th fret become "forever stuck" there, neglecting to learn the other shapes of the same scale all over the guitar.
The above is analogous to starting to read a book, stopping after reading only one chapter, picking up another brand new book, reading only the first chapter and then moving on. It's obvious that by continuing to "read" books in this fashion you will learn nothing. Translated into the world of music, guitar players who practice scales in this way never learn to fully express themselves in music. Ironically, a guitar player who truly masters one scale inside and out on the guitar will have more to say musically (and will be much more creative doing it) than a guitar player who knows 30 different scales "as pieces" (individual shapes) scattered around the guitar.
To see exactly how you should practice scales to learn them all over the fretboard of the guitar, see this free video lesson on guitar scales.
3. Find Out What Scales Your Favorite Guitar Players Use (And How They Use Them)A great training exercise you should do in addition to your regular practice sessions of learning scales on guitar involves listening carefully to your favorite music (and guitar solos in particular) and studying what scales your favorite guitar players use. If you are less advanced in terms of your ear training, you can use someone else's transcriptions (if you trust the transcriber) or figure the solos out by ear on your own.
On top of being a tremendous training drill for developing awesome ear training, this kind of practicing will show you ideas of how you can and should use scales in your style of music to write songs, guitar solos and improvisations.
4. Practice Scales From Side to Side on the GuitarA lot of guitar players spend all of their time practicing scales starting on the 6th string and going to the 1st string in box shapes. This is a fine method of practicing, but it is only one part of what true mastery of scales on guitar should consist of. It is just as important to also play scales from side to side, starting on the first fret going to the highest fret on your guitar. Doing this is essential to having a more complete visualization of the guitar neck as you play. This method of practicing will also help you to start playing a solo on any string of the guitar and know exactly where you are in a particular scale.
5. Ignore the CAGED SystemAlthough this system of practicing scales is advocated by some guitar teachers, no truly great guitar player uses it to master playing scales in music.
Since I do not have time to write a detailed essay discussing in detail every weakness of the CAGED system, I will mention here that the fundamental flaw of this method is that it ignores the principles by which scales are actually supposed to work in real music (and the way they do work for all other musicians on the planet). Instead, the system boxes guitar players into 5 arbitrary box shapes, created out of nothing more than random visual chord shapes that happen to coincide with several scale positions (which incidentally fail to work if you change your guitar to any tuning other than standard). Although the system was designed to be a "shortcut" to guitar players, it was never created to help guitarists truly master the topic of playing scales on guitar in detail.
The good news is that the truly effective methods of learning scales on guitar are actually much easier to understand, remember and master than the inferior CAGED system.