How to Clean a Cloth Mask
Based on advice from the US Center for Disease Control  and the Canadian Government 
You should wash your cloth mask frequently, and at least between each use, and change it as soon as it becomes damp or soiled. Cloth masks can be laundered in a washing machine, provided the fabric you have used is suitable for machine washing. If you are hand washing use warm water and soap or detergent (e.g., clothes-washing liquid or dish-washing liquid), rinse the mask thoroughly before drying.
The mask can also be washed by hand with 2% bleach solution and dried. If you have sensitivities to bleach and bleach odours, don't use this method, wash your mask with soap or detergent instead.
If possible use a mesh bag to protect the mask in the washing machine, handle carefully at all times and check that the shape is retained following washing. Be especially gentle with masks including pipe cleaners or twist ties. Masks should be designed so these can easily be replaced. Do not microwave masks containing metal.
Masks should only be dried in a tumble dryer if the fabric used is suitable for that method of drying.
When you are not using your mask keep it in a clean paper bag in a dry place.
Elastic bands can be washed in the bag with masks. They will deteriorate with multiple washes, but are easily replaced. If preferred, they can be handwashed with soap and warm water, and will likely last longer.
1. CDC advice on cloth face coverings, here.
2. Government of Canada advice on cloth face coverings, here.