What is the best way to thicken and stregthen finger nails?

I have very strong thumbnails, but my other fingernails are usually kind of thin and bend and break easily. I enjoy having my nails long but I am not a dainty, prissy girl so it's hard to keep them from breaking while still doing normal activity. Does anyone know of a trick or product to really make my nails stronger or thicker without drying them out and getting brittle?