Measure the diameter of the opening of the vase. Mark two intersecting lines, each equal to the diameter on the floral foam and cut it to fit.
Spray the floral foam with spray glue. Attach artificial moss to the foam so it blends in with the rest of the arrangement. Place the floral foam at the bottom of the vase.
Measure the height of your vase. Write this number down. Your flowers and vines should not be more than a foot taller than the vase or you may have to glue them to the foam.
Lay out the silk flowers and vines that you plan to use. Cut them to different sizes. The small-leafed vines and the smallest flowers should be the tallest. Using wire cutters, cut the small-leafed vines and smallest flowers between 10 and 12 inches taller than the vase. Be sure to cut them to different lengths within this range so that the arrangement look more cohesive. Set them aside. Take the medium-leafed vines and medium-sized flowers. Cut them to anywhere between six and 10 inches taller than the vase. Again, vary their heights. Take the largest flowers and vines and cut them between three and six inches taller than the vase.
Insert the flowers and vines into the floral foam. Insert the small vines and flowers around the edges. Intersperse the medium-sized flowers and vines throughout the foam. Place the large flowers and vines near the front, with the largest flower in the center. If the arrangement looks too divided by size, switch the placing of some vines and flowers of different sizes until it doesn't look like the arrangement is separated into groups.