Sawing back and forth across your nail tips with a gritty file can cause tears, which then lead to peeling. Use a smooth glass file, and file gently across the edges, says L.A. manicurist Jenna Hipp. A biotin supplement can also help strengthen nails in the long run. Aim for 2.5 mg a day, says N.Y.C. dietitian Lauren Slayton.