Guitar playing skill should be on autopilot
The most important first step to any kind of musical ability is mastering the playing technique on your instrument. whether it's guitar, piano, sax, anything really. One should get as much technique as possible. This may seem obvious, but it is the downfall of many good musicians, that would otherwise have been great.
Forget about playing other peoples music for a while, learning how to play their songs etc.
Okay, there is a small concession to make. If you are using someone else's music for the sake of learning a particular lesson, for example, getting familiar with chords and practicing changing chords faster, then that's still okay. The problem comes in when one learns other peoples solos and runs, guitar riffs etc, but haven't taken the time to really learn the fretboard and scales. I'm going to talk more about the guitar here, because I'm a guitarist, and because guitarists are "My people". Let me just say, that there's no such thing as a rhythm guitarist. Before you get too far along with guitar lessons, you'll realize that the way to be the best rhythm guitarist, is to learn how to play lead guitar as well.
Get as much technical ability going as you can by learning to play scales, in their entirety, up and down the fretboard, so that the various patterns that make up the scales are etched into your memory. You will notice later on how the different chords fit into that scale. This has a very positive effect on your ability to write songs, as well as your understanding of what you are doing within a song. Hone your technical ability to the point where your fingers know what to do, and where to go even before you do.
Half of playing the guitar is confidence
This is where playing guitar really becomes quite beautiful. Get as much technique as you can, and then forget it. It will be that you simply intend for something to happen, and your fingers take care of the rest. The reason I'm telling you all this, is because I have known guitarists who learned other peoples riffs and solo's, could play them perfectly, but when it came time to do their own thing on the guitar, where at a loss because they had a very limited understanding of the fretboard, had only practiced their scales in a few positions on the fretboard or had settled for learning only the pentatonic scale. Be the creative force on the guitar. Why settle for just regurgitating someone else's creativity. Blaze a trail across the fretboard, going where you want, when you want, as fast as you want, without regard for consequence. I have done things on the guitar that I myself couldn't fathom or repeat. that's because my guitar playing is on autopilot.