1. Flowers need fresh water and food to thrive. On average, your flowers will look their best within the first 3-5 days. You'll get a few more days out of your arrangement if you change the water, cut the stems, and feed them again. 

2. Adding a tsp of bleach to the water will prevent "dirty" flowers like zinnias from making your water brown and shortening the life of all of your flowers. This slows bacteria growth and also keeps the water looking clear vs green or brown. 

3. Keep your flowers out of direct sunlight and somewhere cool. Flowers will wilt after they are cut if they are kept somewhere that is too hot or in direct sun. Some flowers or greenery may wilt soon after cutting, but then perk up after being in water for a few hours, so you may want to give yourself some extra time if you are picking flowers for something special so they look their best.

4. Some flowers don't like to be too cold either! Zinnia petals will turn brown if they are too cold. 

5. Cutting flowers at the right time helps you have blooms longer. The best time to cut is during the cooler parts of the day, like the morning or evening. Knowing the most opportune to cut each variety of flower will give you the longest vase life of each flower.

For most flowers you want to wait until the petals are all open and make sure there are not signs of browning petals. Sunflowers and snapdragons need to be cut when they are only halfway open for a longer vase life.