boy! do I ever need to know this one!!
Watering – Another one of the many mistakes that people make with houseplants is improper watering. Overwatering is the number one reason for plant death in most cases. The proper way to water a houseplant is to water thoroughly until water escapes the drainage hole, and then discard excess water. All plants should be watered this way. The key is to know how much the soil should dry out in between. Check the soil before watering. As a general rule, water when the top 1 inch (2.5 cm.) of potting mix is dry. Plants like succulents and cacti should be allowed to completely dry in between, whereas plants like ferns don’t like to dry out at all. Get to know what plants you have and what they like.
Soil and Nutrients – Standard good-quality potting soil is fine for most plants, although some, including succulents, orchids, and ferns, do better in a mix formulated specifically for that plant. Never use regular garden soil. There’s also the common mistake is not fertilizing, which can lead to problems with houseplants down the line. Remember that unlike a plant outdoors, nothing will replenish nutrients in the pot of soil indoors. When it comes to fertilizer, don’t be overzealous. It is always a good idea to fertilize throughout the growing season with occasional applications of a weak, water-soluble fertilizer and cut back or stop during the winter. Some plants, such as African violets, do better with a special fertilizer for blooming plants.
Read more at Gardening Know How: Indoor Plant Problems: Mistakes People Make With Houseplants https://www.gardeningknowhow.com/houseplants/hpgen/mistakes-people-make-with-houseplants.htm