Fill the bottom of the container with a piece of floral foam. Cut or trim the foam with the craft knife to adjust the shape to the container. If the foam may tip over, secure in place with floral tape.
Begin arranging the larger cedar sprays at the bottom of the arrangement. Poke the sprays into the foam at the bottommost layer of the foam.
Shorten pieces of cedar to smaller twigs using the wire snips to trim them from larger branches. Use the smaller pieces as you move up toward the top of the foam. Leave spaces between the cedar for magnolia leaves.
Create clusters of magnolia leaves by wiring two or three leaves together with floral wire. Wrap the wire with floral tape. Fill the spaces between the cedar sprays with the magnolia leaf clusters. Stand back and look at the arrangement as you work, adjusting as necessary to balance the height and shape of the foliage.
Add sprigs of berries, pine cones or other ornaments to add color and variety to the arrangement.