Just wash it with liquid soap (any hand soap or dishwashing soap will do) immediately after use, they're easy to clean if you don't let the soil stay on the fabric for too long.

Rinse well and then put a tablespoon of white vinegar on 1L of water as softener. Wring and hang dry.

Don't use a dryer, don't use bleach, don't use fabric softener, don't use powder detergent.