Yoshida nail files are designed to be used on dry nails. Avoid using them on wet or damp nails, as this can reduce their effectiveness and potentially cause damage. After each use, remove any nail debris, filings, or dust from the file's surface. You can use a small brush, a soft cloth, or rinse it with water. Make sure it's completely dry before storing. To protect the nail file from damage or contamination, store it in a clean, dry place. Consider using a protective case or pouch to keep it safe from dirt and other potential contaminants.