Watering incorrectly is the main cause of plant death. While considering your interior landscape, always remember: more light more water, less light less water. Plants transpire through their foliage like we perspire through our skin. The more light there is the more water is used. You can think of it like a person running versus a person walking. A plant in a lot of light is similar to a person running so that plant needs a lot of water. A plant located further away from a window or near a window that doesn’t get very much sun is like a person walking. It still needs water but it will need it less often.
It is better to water thoroughly less often then to water frequently with less water each time. When you water, the soil should get wet to the bottom of the pot.
Do not water in just one spot of the soil. Water does not move laterally in the soil very well. So when you water, be sure to water the whole top area of the soil, this will insure the roots get an equal distribution of the water.
Remember to fertilize. Any all purpose houseplant fertilizer you find at your local nursery or hardware store will feed the plants. Feed your plants regularly, even every time you water. Just be sure to follow the directions on the package.
A good houseplant service company should be getting these variables right.