Remove the pollen sack from the blossom filament as soon as the flower opens. This will save the flower from being covered in its yellow pollen. Pull the pollen sacks with your finger if the bud is half-bloomed. Use scissors to remove the pollen sack if the bud is fully bloomed.
Cut off any wilted parts of the flower with scissors to allow the other buds to bloom.
Place the lilies in a vase of water and change the water every three days.
Add commercial floral preservative every time you change the water. Or make your own floral preservative by mixing 1/2 teaspoon of table sugar to a quart of cold water.
Cut 1/2 inch off the base of the stem that is underwater with a knife after every water change.