The Hardin County extension office advises:

Poinsettias are extremely beautiful flowers. Proper care of poinsettias after purchase include watering pots thoroughly (to saturation) on a regular basis allowing the potting media surface to dry out between waterings.  

Never let the pot stand in water.  Keep temperatures between 60 and 70 degrees. Place plants near a sunny window, but out of direct sunlight and away from hot and cold drafts.  

Plants prefer high humidity like in their tropical native environment.  The flowering bracts (the colored plant parts are not flowers, but bracts) can stay on the plants for many weeks.