From Health magazine
Avoid midday cutting. Instead, clip flowers from your garden either in the morning or early evening, about an hour after watering. For store-bought stems, remove bruised foliage and recut ends at a slant with sharp garden scissors or pruning shears.
Soak before styling. Place flowers in a bucket of lukewarm water and store in a cool, dark room for a few hours to allow stems to absorb plenty of water before you arrange them.
Fill vase half with 7UP, half with water; add 1/2 teaspoon bleach for every 2 cups of mixture. This formula feeds flowers and fights bacteria.
Prune away. Ditch all leaves below the water line to prevent decay.
Keep it fresh. Swap out the 7UP mixture every two to three days to keep bacteria at bay.