Water-related issue

Each plant species needs a specific watering schedule and techniques. Some prefer a moist environment, while others thrive in drier conditions. You have to follow separate watering instructions for each of your plant friends. This also includes the choice of proper soil and drainage. There are two general tips: avoid too large pots and pots without drainage holes. You can also use moisture meters and water dispensers.

Underwatering is easier to treat. Unless the plant is completely dead, there is a good chance it will recover even if it dropped most of the leaves and looks very damaged. Just return to the proper watering schedule, and the plant should get better over time. Do not stress out the plant immediately with a large amount of water. Consider bottom-up watering. Simply place your green pet in a bucket or on a tray of water for several minutes to absorb the water. This way, the plant will get as much water as it needs. 

Overwatering is more challenging. It might be difficult to save the plant if it is severely damaged. If you think your plant is overwatered, carefully remove it from the pot and check for signs of root rot. Disinfect the cutting tools and trim all the rotten roots alongside leaves and other parts of the plant. No rotten fragments must be left on the plant. Then, remove all soil from the roots and repot the plant in new well-draining soil. Hopefully, your greenie will recover afterward.