Soak a block of floral foam in water, then insert it into your container. Secure the foam to the container with floral putty. The water in the foam will keep the flowers fresh. If you have a transparent container, place a grid of clear, waterproof floral tape over the opening. The grid should look like a tic-tac-toe board so that the holes in the grid help to hold and separate the stems.
Insert the largest pieces of greenery into your container to create the basic shape of the design. For example, create a cone-shaped design by placing a single greenery stem in the center that is approximately twice the height of your container to form the tip. Insert shorter stems at an angle from the tip of the cone downward to form the sides until you reach the base of the arrangement, where the lowest stems are almost horizontal. Space the greenery so that there is room between the stems for the flower blossoms.
Place the largest flowers evenly among the greenery in the arrangement. To keep balance in the arrangement, place the largest blossoms on the bottom of the arrangement, closest to the container opening. For example, if roses are your largest flowers, place the biggest rose blossoms toward the bottom of the design and the smaller blossoms and buds in the middle and top portions of the design.
Insert smaller flowers throughout the arrangement, keeping some separation between the flower blooms.
Add smaller greenery and flowers to fill the open spaces in the arrangement.