Soak floral foam in water and place it at the bottom of the wide-mouthed vase. If the foam is too big, slice it to size.
Place greenery in the bowl first in a criss-cross pattern. These will serve as your base and will also hide the foam. Choose a green leafy plant, such as vinca vines.
Insert the flowers that are most prominent first. Fill with lighter flowers, like baby's breath. Use an odd number of flowers for a more natural look.
Add decorative touches. For example, if you are creating a winter centerpiece, add a snowman figure. Fill 1/4 of the vase with water.