This topic came to mind as I have been auditioning rock and guitar-instrumental tracks to release via the Guardians of Guitar/Mi5Recordings label distributed by the mighty Universal Music Group.
Of course, there is no such thing as a demo these days, and most labels (big, small, and indie) are typically seeking masters that can be released as is and ready to go.
In many instances, I don't have a huff at all with the musicianship when I'm looking to be thrilled by a submitted track. It's so awesome that so many players can really burn with passion, conviction, and kick-ass technique these days.
But while accomplished musicianship is certainly a groovy thing indeed, musicianship alone won't get me all excited to share your creations on my little label.
After all, both the label and the artist want a chance to make a few bucks—not that ANYONE is really pulling in massive amounts of cash for distributing rock songs and guitar instrumentals at the moment—so the promise of commerce weighs heavily on signing decisions. And being musical AND commercial can be a tough go.
The following is totally subjective blather ignited by my own brain, of course, but I'm the label dude, so I guess my blather has a bit of an impact if you want to be a Guardians of Guitar artist.
That said, I also interact with a ton of label professionals and hear what bugs THEM about submissions to their companies, so even if your dream is to sign with SONY or CAPITAL or YEP ROC, these tips may apply.
HERE ARE FIVE WAYS TO GET ME TO SAY "NO" TO YOUR RECORDING
 Give me something that's not even remotely a SONG. Disconnected jamming and awesome displays of shredding do not usually invite mass appeal and the resulting win-win of purchased downloads by more than six guitar freaks. Great SONGS are the currency of the music business. We want those. Don't know how to write a song? Happily, there are tons of examples on YouTube from most eras of the recording business. Deconstruct that stuff. Steal from it. Amend it. Make it your own. And study, study, study. BUT PLEASE: Do not send me something I won't even remember 47 seconds after I've heard it. EXTRA TIP: Make sure you aren't lying to yourself about what a song is. I've had several guitar instrumentalists tell me something like, "Man, I get it. My music is like the Beatles—tons of hummable melodies." And when I listen to their stuff... Well, let's put it this way: THERE AIN'T NO GOSH-DARN MEMORABLE MELODIES PRESENT AT ALL!!!
 Present a track so washed in reverb that it's drowning. I'm not anti signal processing at all. Savvy use of effects can really bring a track to life. But if you murder the sonic landscape with tsunamis of reverb and delay, so much so that I can barely hear the glory of your work amidst all the foggy stormy muck of ambience, then I'm gonna pass. Here again, if you listen to YOUR favorite tracks by bands you dig, you will likely be surprised that they are actually drier than you might have conjured up in your mind. Too much reverb affects more than a guitar or a vocal—it can also muddy up the relationships between drums, bass, keyboards, and percussion. It kind of sticks to everything. Whenever I hear reverb-slammed tracks, I immediately say to myself, "This isn't professional. Pass."
 Make sure that distortion and audio gremlins are loud and clear. There's no credible reason to present a label professional with a recording that presents clicks, glitches, crackles, non-musical buzzes, or other audio anomalies. Listen critically to your track to ensure that the results of improper gain-staging and/or any weirdness caused by software demons are terminated with impunity. Deliver pristine, clean, and awesome tracks that I can release immediately.
 Pummel me with muddy low end. I love taut, round, warm, and banging bass. I detest washy, muddy, booming low end that totally distracts me from enjoying a recorded work. Yes. Many modern audio productions do push the bass. But LISTEN. Is that bass muddy or too boomy? And I'm not talking about drastically boosted low end from the intense, bass-heavy music lover in the car next to you at a stoplight. I'm talking about the audio spectrum you present to me. Reference your tracks to recordings you admire, and determine if your low end is cool and appropriate, or so over-the-top that it threatens to devour your song.
 Please include sub-standard performances and obvious mistakes. NOT. Now you'd THINK this would be a no-brainer. Ha! I get tracks all the time with off-pitch vocals (lead and background), fractured tempos, laughable clams, and a whole toy chest of awful. Did they not HEAR these things? Did they think I (or anyone else) wouldn't hear them? I simply can't fathom sending an industry professional tracks with obvious miscues. I would call myself a liar that this even happened, because it's so unthinkable as to be actually true, but I have proof. It's real. Please don't be that person. Produce goodness. Seduce ears. Don't blow it all with a horribly off-pitch vocal or a blitzkrieg'd guitar line.