In the box you'll find with the flowers you received, an envelope of nitrates. Put the content in the flowers water. Nitrates provide nutrients to the water to help preserve the flowers longer.
Cut the stems about an inch possible in oblique. The stem end dries out during transportation and does not absorb nutrients. By this simple operation will feed your flowers properly.
The stem leaves should never be in the water. Cut the lower leaves carefully.
Try to keep the flowers in a cool place away from sources of heat or cold as the sun, heating, air conditioners, electrical appliances.
Try to change the water in the container about every two days.