How you file your nails can make or break them—literally. “Filing in one direction, lifting the file each time on the return stroke is the best method to prevent damage or breakage,” says Jin Soon Choi, founder of Jin Soon Hand and Foot Spa in New York City. “The most important thing is to choose the right grade file,” she explains. “If you use a very high grain file, it’s going to cause breakage, but if you use a fine grade file (like 400 to 600 grit) and do not file aggressively, you can file in a back and forth motion.”