1- Use common whitening toothpaste. Try scrubbing your nails with Pearl Drops, it's just as easy as achieving a pearly white smile and will take away any stains and shine up your nails.
2- Soak your nails in water with lemon juice or lemon slices. The lemon acts as an astringent and will strip away stains. Once your hands are dry, you'll only need to put on a couple of coats of a clear topcoat.