Remove any leaves and foliage from the lower part of the stem that will be underwater when the tulips are placed in the vase.
Trim off the lower, white portion of the tulip's stem. Doing so will improve the cut tulip's ability to take up water.
Change the water in the vase often, and make sure there is plenty of water. Clean, fresh water is the most important thing you can do to keep cut tulips looking fresh.
Hold the cut tulips under water and trim about an inch off the stems every 4 or 5 days. This will ensure that the tulips are taking enough water.