change the water every other day using plant food packets provided
make a fresh diagonal cut using a sharp knife when changing the water
keep stems below the water line clean of leaves, leaves left under the waterline lead to decay and bacteria building up in the water
keep flowers away from direct sunlight or any other source of excessive heat and away from fruit if possible (ethylene gas released from certain fruits shorten flower life)
store in cool place overnight
remove any flowers that, with time, look less than pristine, as this will keep the remaining flowers looking fresh