Guitarists Keep Their Nails Short
Be an individual.
When I took my first guitar lesson as a teen I realized right away that my fingernails needed more than the standard manicure. The painted fretboard registered several scratches until I learned how short to keep those left hand nails. How short do we keep them? Very short. Clip them as close as you can without cutting into the quick. Now on the right hand we do not need them to be this short. More on that later.
Classy and recognizable.
Guitarists have a secret code known only to each other. I am letting you in on this: look at the left hand if you want to identify a guitarist. That's a giveaway, although there are a few rebels who manage to play with longer nails. Hardly anyone will keep only the left hand nails so short unless he or she plays a stringed instrument, and usually it's guitar. One guitar player can walk right up to another and begin chatting away about chords and strings without asking the preliminary question, "Do you play guitar?"
Right hand nail maintenance.
On the right hand guitarists allow a little length, especially if they do any fingerpicking. Fingerpicking is a delicate and delightful method of playing. Natural nails work best, although some people do very well with specially designed picks worn on the fingers' ends. Excessive length is not desirable, as really long nails will only get in one's way. A good rule of thumb is, "Long enough to reach the strings, but not enough to slow me down."
Callouses make it easier.
When you've been playing several weeks the left fingertips will all develop some splendid callouses. Oh, yes, it hurts a little at first until they develop, and there is no shortcut around it, so if you're afraid of a tingling sensation in your fingers, don't buy that guitar. But it's really not that bad, and it doesn't last very long. Once your callouses develop they go very nicely with the shortened left hand nails and identify you as not only a guitarist, but as a seasoned guitarist who practices regularly.
Two short concluding tips regarding this: use a little hand lotion every day to keep the callouses from drying out, and don't play right after activities involving water such as washing dishes by hand, or swimming. The highest two strings (E and B) can cut water logged skin, resulting in injury.
But there again, very few musicians have been known to play their guitars in the bathtub.