You may start by placing your foliage that you will use in a water vase. You have to make sure that you keep it around the lips or edges. Stick with the plan to place them the lips or edges of your water vase with a layer of your Foliage. When it is too big or too thick, it ends up detracting from your cut flowers. And if it is small or too thin, visual contrast will not show.
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.