How did I learn guitar?
I first picked up the guitar when I was thirteen. I was inspired by my best friend in middle school and also by all of the grunge on my computer. It quickly became my main passion, and I was easily practicing up to four hours a day. So what did I practice, and how did I learn?
Books, yes books. I quickly developed a habit of studying from music books everyday. I bought tabs and notation on Jimi Hendrix, Red Hot Chili Peppers, Wes Montgomery, etc. Many artists spanning all genres. In combination with the CDs they came with, these notation and theory books helped me to understand the why and how behind music that one can easily miss if they just play along to the music.
It also challenged me to play along to pieces that were way above my talent level, and to try and grasp advanced theory even when I knew that it would be difficult. Even today I still try to learn theory and music from different books and chord sheets. I find that it keeps my technique and mind honest, and my playing sharp.
So, to the beginning guitar player and to the accomplished: I recommend notation and theory books as a way to make the most of your practice time.