I found this in an old thread in the forum, but I have found it to be remarkable advice, and so I'm bringing it to the fore as an offering to all those who have not yet heard it. It really has improved my tone immeasurably.
1. The correct nail bevel is important. Wrap a piece of 400 grit sandpaper around the 1st E string and then hold the guitar as if you're going to play it. Pluck the string with the i, m, a fingers until you see a flat area. You want a flat area about 1/4" wide for plucking the string. Use fine grit file / paper to finish the nail and round the edges. Repeat the above procedure by putting the sandpaper on the 6th E string and pluck it with your thumb until you get the obvioius flat area. Enlarge to 1/4", round, etc.. This is best way to get custom nail angle for yourself.