This is what I did:
I gathered my supplies: a ceramic container, a scissors, a knife, wet foam (I puchased a package on sale from Michaels for a centerpiece I made earlier), water, fresh flowers, greenery, and Baby's Breath.
I used the knife to cut the foam to fit snuggly in my container. I poured water on the foam until it was well soaked. I then cut Lilies 10" tall and stuck them in the center of the foam. I keep my centerpieces low so that guests can easily see over them.
I cut other flowers 10" tall or shorter inserting them in the foam at an angle from the center.