Most houseplants do well in average house temperatures. To encourage best growth, turn your thermostat down at night. Plants like a 10-degree temperature drop after dark. This drop duplicates what they experience in nature.
To grow plants that like cool conditions, keep your thermostat between 60 and 70 degrees F in the daytime, lower at night. Many plants that go dormant in winter prefer cooler temperatures. For plants that like high temperatures, set your thermostat in the 80s during the day and lower at night.
Maintaining the desired termperature is especially important to flowering plants. Azalea and Christmas cactus need temperatures near 30 degrees F to form buds. Other tropical bloomers need high temperatures to flower freely.
No houseplant wants to freeze or bake. Prevent cold drafts near plants. Keep plants away from cold windows in winter. Don't let houseplants summered outside freeze in a late-spring or early-fall cold snap. Keep plants away from radiators and hot blasts of any sort.