Select roses, from the garden or the florist, that have long, straight stems and buds that are firm at the base. Reject buds that are soft, wide open or tightly closed at the top. Use garden clippers for cutting garden roses, retaining as long a stem as possible without cutting into the supporting cane.
Plunge roses into a bucket of fresh, room-temperature water immediately. For garden roses, carry the bucket and place roses in water as they are collected. Allow the roses to "drink" for several hours.
Fill the vase two-thirds of the way with room temperature water and optional floral preservative. For a one-rose vase, use 1 tsp. preservative. For larger arrangements, use up to 1 tbsp. preservative.
Remove one rose from the bucket. Snip the foliage off of the stem below where the water level will be in the vase. Clip close to the stem, but do not clip into the stem's skin. Remove the thorn tips by snipping them off with scissors or slicing them off with a knife, without cutting into the stem's skin.
Hold the cleaned rose with its stem end under water in the bucket. Slice at least ½-inch off of the submerged stem end at a sharp angle.
Place the rose immediately in a prepared vase and arrange as desired. Change the water daily.