Single, larger blossom flowers, such as roses, carnations, zinnias, tulips or lilies, usually make up the focal points of a piece. Taller stems with multiple flowers can balance things nicely. Delphinium, gladiolus, and snapdragon are good examples of flowers that can add extra height and texture. "Filler" flowers, or stems with many small buds, are great for topping of a bouquet with a full and delicate look.
You could create an arrangement for any size vase, the larger the vase, the more flowers and greens to use. For Christmas time, use red, white and maybe even green flowers (like green button mums). Also choose from a variety of greens and evergreens out there. Accent a red rose in a bud vase with some baby's breath and cedar. Deep red alstroemeria are especially beautiful. There are many other flowers that would be perfect to use for Christmas arrangements, the link below will take you to a complete list of flowers, foliage, and evergreens for Christmas floral design.