Good cleaners for acrylic showers include gel-based cleaners, liquid dish soap and granular cleaners diluted with water. Soft cleaning supplies such as cloths and sponges are best to avoid scratching the surface of the shower.
Choose a granular cleaner that isn't too abrasive. Regular liquid detergent works well when combined with warm water and a soft sponge to wipe down the shower. For bigger stains and problem areas, use a gel-based cleaner that is labeled specifically for acrylic or fiberglass surfaces. Apply it with a dry cloth, and rub it into the areas that need to be cleaned. Let it dry, then rinse it thoroughly.