Rinse the retainer with lukewarm water
Gently brush it with a soft toothbrush and mild liquid soap
Soak it in a retainer-cleaning tablet solution as directed on the package
Soak it in a 1:1 mixture of white vinegar and lukewarm water for 15 to 20 minutes
Rinse thoroughly with lukewarm water after soaking
Use a denture-cleaning solution if recommended by your orthodontist
Avoid hot water
Avoid bleach
Avoid abrasive toothpaste
Store it in a clean, dry case when not in use