Cut your stems with a sharp pair of scissors or snips before placing them in fresh water.
Find a home for your flowers away from heat, direct sunlight and strangely enough, that bowl of fruit (close proximity to fruit actually causes flowers to wilt their petals faster)
You can keep your flowers fresh longer by changing the water as it becomes cloudy, adding flower food, and removing wilting stems before they affect other blooms.
The beauty of flowers is that they each shine in their own time - some will open up before others.
Arrange your hand-tied bouquet in your favorite vase or spread the love and make a few bud vases to scatter throughout your space.