I've been blessed with great nails, but I've watched other guitarists in my studio use ping-pong balls, crazy glue, press on nails, commercial nails (made for guitarists) and you name it.

My main guitar is a steel string with a classical width neck. I trim my thumb at an angle to accomodate a balance between flesh and nail, my fingers are trimmed to match. I also use fine sandpaper to finish my nails after filing.

I'm worse that vanity when I break a nail, usally involves long hours of psychotherapy, which may not be a bad idea for the nailbiting either.