Centre of attention! Calathea need plenty of attention to look their best, particularly when it comes to humidity and watering. Check in with your plant frequently as negative changes can happen quickly. Brown tips are common.
Might that be Mites? Calathea are very susceptible to spider mites, which are not usually spotted until it is too late. Routinely check on the underside of leaves to see if there is any webbing along the veining.
Wipe leaves with a damp cloth to remove accumulated dust. Do not use leaf shine as this will damage the foliage.
Light
As with most variegated plants, Calathea need plenty of diffused light. Direct sunlight will cause the leaves to fade and lose their markings. They can tolerate some degree of shade, but the more indirect light, the finer the foliage.
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. Think 'little and often' as a watering policy.
Prefers warm to high temperatures, ideally between 18-23°C, but can cope with as low as 15°C. Avoid draughts and ensure the plant has reasonable ventilation.
Humidity
High humidity levels are a must. Mist frequently to improve humidity conditions and pop it near the shower from time-to-time to give it an extra boost.