An ancient Greek discovery found that the division of a line somewhere between one-half and one-third of its length is most desirable, according to Phyllis Allen and Miriam Stimpson, authors of "Beginnings of Interior Environment." This is called the golden mean. Following this principle would dictate that a wallpaper border should be placed roughly between 32 and 36 inches from the floor in a room with 8- to 9-foot ceilings. A room with a higher ceiling (10 to 12 feet) would benefit visually from a border placed 3 to 4 feet from the floor.
Another option is to position the border just below the ceiling or crown moulding. If the ceilings are high (9 to 12 feet), dropping the border 36 to 48 inches from the ceiling brings this decorative feature more within normal viewing range.
Consider the Room's Function
How is the space to be used? In a nursery, for example, you may want the border to be most visible to the child who will occupy the space. Hang the border slightly above crib height, or down low, approximately 24 inches from the baseboard within the child's scope of vision.
There are no absolute rules. Use basic design principles as guidelines, then hang the border where this interesting feature is accomplishing its mission--jazzing up your interior.