I got these directions with some flowers one time, and I think these are good so I’ll share with you:

• Start with a clean vase.  (I clean my clear vases in the dishwasher.  If I can’t do that, then I’ll soak the inside of the vase with white vinegar and water.  Martha Stewart said one time that flower vases should be clean enough to drink out of – that’s before the flowers are added.)
• Use warm water to fill the vase.
• Add flower food to the water.
• The next part is real important.  Remove all foliage below the water level.  (Otherwise, the leaves will start to rot in the water and the flowers won’t last as long.)
• Recut the stems on an angle.
• Place flowers in vase and enjoy!
• For long lasting flowers, change the water and recut the stems daily.