This may seem strange due to their holiday connotations, but poinsettias are tropical plants. Provide lots of sunlight — a sunny window with east, west, or southern exposure is best. Also try to keep the temperature between 65 and 70 degrees during the day, keeping in mind that the area around a drafty window can be quite a bit cooler than the rest of the room. If your plant’s leaves are touching a cold window, they may drop off. At night, poinsettias like a slightly lower temperature (55 – 60 degrees), but avoid drastic drops in temperatures.
Make sure to water the poinsettia whenever the surface of the soil feels dry. Give the plant a good watering, but don’t flood or soak it — gravel in the bottom of the pot will help keep the roots dry. If your home is dry during the winter months, a humidifier or plant mister can help your plant stay hydrated.