One of the most important factors when conditioning flowers, is making sure that you buckets are clean! Bacteria, fungi and plant debris in vase water can block the flowers stems and prevent water uptake.
The bacteria can grow rapidly in a vase of water, so it is important to clean the buckets and vase after use and to use a biocide (found in most flower food/ preservatives) to help control the growth of the bacteria.
It is also important to make sure your tools and equipment are washed and cleaned thoroughly after use.
For the longest flower life, the water should be changed regularly (every three days) with flower food.