Calatheas are native to the tropics, therefore they prefer humidity and warmth. There are various ways to keep your Calathea's humidity levels high, but the simplest is to mist it regularly, ideally once every two days. But the best way is to get a humidifier.
2. Water Quality
Calatheas are much more demanding when it comes to water. If your Calathea leaves are browning it's because they prefer to drink filtered or dechlorinated water rather than tap water! Whilst Chlorine makes it safe for you to drink tap water, plants don't need it. No, you don't need to buy bottled water for especially your Calatheas but you should water with water that has been left out overnight to allow all chlorine and other contaminants to evaporate.
Every Calathea species is unique, and they all require varying amounts of watering. Pop your finger in the soil to see if it needs water, and only water when the soil is slightly dry. If your Calathea is exposed to prolonged periods of dryness, it will develop dry, shrivelled, or curling leaves, and its soil will need to be soaked!
Calathea have amazing leaves however, this means they are prone to collecting dust and dirt. This can prevent photosynthesis and attract pests. Remember to gently wipe down your plant's leaves.