Taking hair, skin, and nail vitamins always worked for me. They help strengthen and thicken your hair and nails. Any store with a vitamen section usually carrys them.
They also sell nail strengthening nail polishes that contain vitamins that can help them.
I heard if you put vegitable oil on them, it'll make them stronger so they won't break and chip.
Vitamin B will also help.
Drink more milk helps.And nail strengh pollish :)