1. Prep The Flowers: Fill a tub with 6 inches of lukewarm water and mix in some floral food. Most flower bouquets come with floral food, check the packet for instructions. You can make your own if need be, by adding one tablespoon of sugar and a few drops of bleach to each gallon of water. Then add the flowers.
2. Cut the Stems: Get rid of leaves or thorns on the parts of the stem that will be submerged in water to prevent bacterial growth. Remove excess buds, and with all lillies use a tweezer to remove the antennae that hold the pollen. This will give your lillies longer life and save your table from the pollen. Next take your garden shears and cut the stems underwater at least an inch or two from the bottom at a 45 degree angle. This allows the most water absorbtion and prevents a stem from sitting flat against the vase bottom.
3. Put the Vase In the Right Spot: Don’t leave flowers in a drafty place, in direct sunlight, or on top of a television set. They will dry out and fade fast.
4. Maintenance: Wilted flowers can zap the life out of fresher flowers, so pull out faded blooms as soon as they appear. If the water looks cloudy, change it. Wash the vase, refill it with water and flower food, and then recut the flowers.
For a great book on keeping flowers fresh, Visit Flower Staying Power, How to Make Your Cut Flowers Last Longer.