I recently started using a cream called Sudocrem on psoriasis spots. This seems to have the side-effect of improving my nails, which is nice! It's got various stuff in it like lanolin which presumably helps make them more flexible and resilient.

For me, the main thing to remember is to keep them filed fairly short. For classical guitar, fingernails are usually level with or only very slightly (a couple of mm) longer than the fingertip, because much of the tone comes from using flesh *and* nail together. If they're not insanely long, there's less to break.

Also file them regularly. As they get longer, the tips wear down and the nail gets thinner on the end, so it's more likely to break. And like breaking a glass, once there's a crack then it'll spread. I've also found that filing seems to be better than clipping - it gives a smoother "edge" to the nail which sounds nicer, and there's none of the hard edges you can get from clipping, which again would give a split somewhere to start.

And don't bite them, otherwise they'll just get weaker. I used to (for the last 20 years), and it's taken several years for my nails to toughen up again since I stopped.

Graham.