There's a constant battle in the pedagogy of guitar—technique versus music (songs).
Specifically, there are many who play guitar for the sole purpose of learning songs by other artists, and then there are guitarists who advance their skills by focusing on a technique- and theory-based approach.
Many students have come to me over years with the same problem; they can play a few songs (and perhaps quite well), but they have no understanding of what they are doing and they feel like they’ve hit a brick wall. This is a very common plateau I believe many “self-taught” guitarists hit.
Students who try to teach themselves typically do not possess the knowledge of what technical material needs to be covered. Rather, they learn what they want to learn, regardless of difficulty, and this can create inefficient practicing and playing habits that are very difficult to break.
Does this mean students should play only technical material, such as an endless array of scales and arpeggios? Definitely not. But as students develop, they need to incorporate technique and theory into their practice, just as any instrumentalist would.
So what techniques need to be covered? As with any polyphonic instrument, the basics are scales, chords and arpeggios. While a purely technical focus can seem daunting and dull, there are basic fundamentals that can make playing and learning the guitar so much easier.
In the “classical” world, composers would oftentimes write musical studies called “etudes.” These pieces would generally be musically pleasing, but the sole purpose was to develop an instrumentalist’s playing technique. Examples of these can be seen in classical guitar music, where many pieces have the same right hand arpeggio pattern that remains constant throughout the entire piece.
Modern music that is written for performance doesn't