For a good vase life:

• Use a clean vase, preferably made from glass. Clean carefully with a little bit of chloride to kill bacteria. Growth of bacteria is one of the major causes of weak necks of roses, so it is important to prevent this.
• Cut off the roses at least 2 cm with an angle with a sharp knife. While using a sharp knife, damage of the stem is reduced.
• Take care that no leaves are hanging in the water of the vase, because this can stimulate growth of bacteria. Only remove the leaves and not thorns, to avoid bacteria growth stimulating wounds.
• Always use flower preservatives. This is often added in a small package, or ask your florist. This flower preservative not only gives energy to the flowers, but also reduces growth of bacteria, resulting in cleaner vase water.
• Don’t place the vase with flowers in drafty or windy locations.
• Avoid direct sunlight or the vicinity of source of heat.
• When you follow up these recommendations, you have the best chance for a long vase life