Watering:
Calathea must be kept in damp soil at all times, but definitely do not allow the plant to sit in water or in very wet soil.
Fertilizer:
Apply any organic fertilizer once or twice during the growing season.
Re-potting:
After that, every 2 or 3 years and preferably in spring, re-pot your Calathea in a pot of a slightly larger size.
Temperature:
Prefers warm to high temperatures, ideally between 18-23°C, but can cope with as low as 15°C.