Mike Mahar wrote:
In fact, I can think of only two things that must be done correctly. One is the fret spacing and saddle placement. If you get that wrong you can't play the instrument. At least not western music. The other thing is that the guitar must stand up to the stresses placed on it. If you get that wrong the instrument will break. Everything else you can change and somebody already has.
Oh, I don't know. You'd be surprised at just how many instruments have fret and saddle placement significantly out of place, and just how seldom it is noticed by players. Standing up to stresses is a grey area too, as how much distortion over what period of time holds a pretty wide range of acceptance depending on the instrument and the owner.
Dave's points are good for beginners, but I don't know that I can point to any ultimately reliable resource. The forums, books from respected authors, advice from experienced experts - these all contain just as much information that ranges from questionable, to bad, to outright irrefutably wrong, as do the videos.
The best thing you have to rely on is your brain, and tuning up your reasoning skills (certainly not a guaranteed intuitive function of the mind) is your best chance of being able to filter out the crap and choose wisely what sources and advice to trust. Experience directly in the field certainly can't be replaced, but being reasonably conscious and critical of all you take in is the only way to make sure that experience isn't a wasted effort.