Many plants prefer higher humidity than is usually found in a home. Tropical plants are healthiest with relative humidity around 50-60% -- far higher than many homes.
In the winter months, my home can feel extremely dry, especially with the furnace blasting hot air into the room and the fireplace blazing. This kind of arid environment is okay for a cactus -- and me. But for house plants that have origins in the tropics, I have to increase the moisture content in the air around them.
Now the talk gets a little steamy...
Short of buying a whole-house humidifier, there are several easy ways to increase the humidity level for your plants:
A humidity tray with pebbles allows you to use pots with drain holes without worrying about excess water pouring out and damaging furniture. The overflow will collect in the tray where the settled water will evaporate, surrounding the foliage with moist air. Care is easy -- just wash the tray and grid with mild soap and water occasionally, then refill with water.
How do you know if your plant is suffering from low humidity? It will tell you. Here are some things to look for: