Here are some common missteps most guitarists seem to make along the way:
A lot of folks mistake being a good guitarist with being a good musician. The two are not necessarily linked. If you want to make an impact, learn how to write good songs. There's an unlimited number of hot pickers that cannot write a good song and a ton of hot pickers who cannot make a dime from their skills because all those hot licks fail to add up to anything substantial.
Further, a lot of capable musicians cannot make the transition to earning money from their music because they fall under the illusion that good music speaks for itself. Wrong. If you want to have a music career, you'd be better off getting degrees in business and consumer psychology. Music is one thing, business is another.
Failure to look the part. If you want to be a rock star than look like one. How many guitarists show up wearing shorts and running shoes to a gig and then wonder why nobody takes them seriously. You have to stand out, look like a freak, not like some average schmo at convenience store.
Learn a lot of popular songs. Learning more licks and tricks will not help you become a better musician. Take the time to learn how to compose, arrange, read music, transcribe, and communicate with others using musical terminology and notation. And learn music theory as well.
Learn to sing. Your hot licks will not add as much to a band as you imagine. Being able to sing or just provide backup vocals will make you more valuable.
A lot of players start by learning the blues form and fail to move on to other genres. I think it is vital to know how to play blues music because it forms a solid foundation for Western popular music but most self-identifying 'blues' players are just lazy dolts who never learned anything else or too unimaginative to go beyond the most basic things. Lack of versatility and a lack of an open mind mean that most players will never create anything of lasting value.
Most players spend way too much time learning how to solo when 90% of the time guitarists are playing rhythm parts.
Stringing together one prefab lick after another does not make a good solo. Most guitarists have a 'lick' mentality and cobble shit together hoping it will make a coherent solo. It will not. You need to think MELODY and developing motifs. You should strive for hearing a melody line in your head and making that line come out on the guitar "at the speed of thought." If you're not working toward that goal then you're just playing notes. Take Satriani for example: this pick scrapes, squeals, and whammy bar tricks do not pay the bills, rather, it all comes down to catchy melodies.
It's important to learn scales but don't waste time playing them. The key to knowing scales is to learn the intervallic characteristics. Time spent on scales would be better utilized learning how to identify intervals all over the neck of the guitar such that, for example, if you're playing in the Key of A, from any note on the fretboard you should know how that note relates to the fundamental and the relationship of ever other note to the fundamental and the note being played. So, if I'm playing the note at the 9th fret, third string I need to know that it is an E, that it is the perfect 5th of the tonic, and that if I play a major third higher than the E, 9th fret on the 2nd string, I'm playing the major 7th note in the key of A (and that note is G#)....and if I lower the major 7th by a half step then I have introduced a dominant or flat 7th tonality and that the resulting sound will want to head off into the direction of D major and then back to A or maybe E or E7. That's what you should be getting out of scale and harmonization practice. Likewise, if I 'need' some notes from a little pool that contains a major third and a major seventh I have a couple of options. If I go with the major scale I'm going to keep going in the direction I was going. If I call up that raised fourth from the Lydian I now have the opportunity to take things in a more roundabout way, either a detour to another key or just round off a corner by way of getting back to where I was.
Most guitarists are locked into the boxes created by frets and don't realize that the real magic happens with micro bends and playing 'between' notes. It is quite possible to play between a major and a minor third with tiny bends that lend an entirely different sound: a little bit major and a little bit minor simultaneously.
Overplaying is a serious problem. Despite some notable exceptions, blazing fast guitar solos rarely have a place in a song that is going to have wide appeal and most audience members at a gig will grow bored very quickly with masturbatory guitar wanking. Just stop doing that. It's not even possible to impress other guitarists with that stuff.
Neglecting other instruments. There's more to life than guitar and one of the best moves you can make is to learn piano, drums, horns, etc., in addition to guitar. The world is full of guitarists but paying gigs come to drummers and bassists with a place to practice. However, we (most of us, anyways) have limits and need to know where our strengths are. I have been part of several bands that could have been good but sunk because guys wanted to run away from their strengths: killer bassist who wants to sing and play the guitar and does both terribly; great drummer who wants to write lyrics, and so on.
Most "guitarists" are actually just guitar owners who sit around their den noodling on their guitars for a few minutes per night, hearing their axe abstracted from any musical context. What sounds good in your den, by yourself, will seldom work with the rest of the band. Forget about "tone."
People worried about "tone" are typically just people who have just given up on music. Once a person is marooned on the Island of Tone they can just flounder there for the duration making zero musical impact. Better yet, they can argue endlessly about it on guitar internet forums where their lack of skill or musicality is masked by a pseudo-authority centered on something purely subjective and irrational.
The goal as a musician, like any other art, is to add something new to the world. Your "tone" is not something objective you add to the world like good lyrics or a memorable melody."Tone" is an excuse to not add anything new to the world. Still, you're going to have a tone just by pursuing your quest. Don't quest for tone, let it find you.
Failure to use the whole range of the guitar, from top to bottom, and all the harmonics as well.
Failure to use tone and volume knobs. Use the knobs or be a knob.
Tone is not "in the fingers" but both hands. Your picking hand probably contributes as much if not more to your "tone" than your fretting fingers. Most players spend all their time trying to figure out how to positively make sounds with their guitar and not enough time, negatively, learning how to subtract sound (really, unwanted sound) from their playing -- i.e., how to mute strings effectively and alter timber through various muting techniques.
Thinking that guitar skills translate into bass skills. Few things in life are as unpleasant as playing with a guitarist who thinks the bass is just a guitar missing two strings.
Most players wait too long to play gigs because they think they're not good enough. There's no time like the present. No matter your skill level, you need to get out and play with others.
Focusing way, way, way, way, way too much on gear. I mean, way, way, way too much. A guitar (just about any guitar) and an amp is enough to get the job done. I know, you spend all your time on The Gear Page and imagine you can gear night and day differences between the various brands of expensive cables but you're just full of shit. Another guitar will not make you better.