To keep your clear retainer clean, you should brush it gently with a toothbrush and toothpaste after each use, avoid eating or drinking anything other than plain water while wearing it, store it in a secure case when not in use, and never wrap it in tissue as this can cause it to warp. Additionally, you should avoid any activities that could damage or bend the retainer and always consult your dentist before making any adjustments on your own.