Put stems in a pail of lukewarm water as you cut them. Recut stems on a slant indoors under water to eliminate air bubbles that block food and water uptake. Remove bruised leaves and foliage below the water line to prevent decay. Where advised, scald stem ends in boiling water for 20 seconds or over a candle flame to stop nutrient-rich sap from oozing. Condition flowers several hours before arranging.
Rest stems in lukewarm water in a dark, cool place, so they can absorb water.
Don't store flowers near unsealed fruits and vegetables, which produce ethylene, a gas that hastens ripening. Freshly cut flowers have enough stored sugars to survive in a vase. Increase proportionately if you need more liquid. Change water every couple of days. In mixed bouquets, flowers may give off sap toxic to other varieties in the vase.