Tinks, my nails weren't up to much until I asked a friend how she kept hers so beautiful. The answer? Scrub them. Sounds daft, but it works. Every time you wash your hands scrub your nails very gently with a nailbrush, gently push the cuticles back, and keep your nails well polished - and voila! They will grow. I think it's because you are consciously taking care of them all the time. I've had lovely nails for years now - even though I do say so myself! ;o)
I use emery boards to file - but never harshly - always gently.