The number one cause of dead houseplants is overwatering!  Watering "schedules" are a good way to remember your green friends, however not all plants are alike.  Water necessity is based upon the soil type, plant specimen and temperature of area where pot is located.  Check out the plant tags when purchasing for detailed information.  The potting soil should look dry and pot should feel lighter when it is in need of water.  Do not let the plants get to a point where they are wilting.  Water thoroughly through the plant until the water drains out the bottom.  Make sure to empty the saucer of the excess water an hour after watering, these are nesting grounds for insects and can cause the plant’s roots to rot from absorbing too much water.