Make sure to always keep your vase filled with water containing the flower food provided with your arrangement.
If the flower food solution ever becomes cloudy or murky, replace it with new, properly mixed flower food solution.
Always try re-cutting stems by removing one or two inches off the bottom with a sharp knife or sharp scissors and immediately placing the stems into the food solution.
Make sure to try and keep flowers in a cool spot away from direct sunlight, heating or cooling vents, directly under ceiling fans, or on top of televisions or radiators. Most flowers will last longer under cool conditions.