Hang them upside down and let them dry naturally. Unwrap the roses as soon after receiving them as possible. Remove all leaves that will be in water. Cut about one inch off the stems. A packet of floral preservative often comes with cut flowers.
Floral preservative can extend the useful life of cut flowers, sometimes even doubling the time.
If no preservative is available, a homemade version can be used. Check water level daily. Change water, recut stems and wash stems and containers if water becomes cloudy. Place the arrangement in the coolest place available for display. Refrigerate flowers when not on display.