Healthy Nails Tips

Use non-acetone polish remover.
Allow nails to 'breathe' without polish a few days a month. Buffing with a chamois buffer during that time helps circulation and gives nails a nice sheen.
Massage a nail-and-cuticle cream into fingertips every night.
If you are prone to brittle nails, do not use any polish or treatment formula containing formaldehyde. Give your nails a treat with a 10-minute soak in olive oil or wheat-germ oil. Wipe off and massage the excess into cuticles.
Get enough calcium, iron, zinc, protein and vitamins A, B and C. You already knew this, but it's still true. Evening-primrose-oil supplements are pricey but will strengthen nails.
Any overly pronounced ridges could be the mark of a fungal infection. See a doctor at the first sign; fungi are stubborn and need long-term treatment.
As always, keep your stress level as low as possible. Stress affects every aspect of our appearance, and often that deep ridge is telling you something.