Source: Martha Stewart Living, July 2006
We used about 4 yards of inexpensive fabric for a 7-foot section of railing; keep in mind the material's width will determine bunting height (ours was 44 inches, for a swag with a 40-inch drop). It's best to overestimate how much fabric you'll need because extra material can be gathered at corners when bunting is hung. Use fine steel wire to hang bunting from railings; in an entryway, attach small nails to frames, and wrap wire around nails.
Hold fabric horizontally; make 2-inch-wide accordion folds across its length. To keep pleats in place, staple gathered fabric several times, about 3 inches from one edge. Wrap wire around stapled section; trim wire, leaving enough to hang bunting.
Center gathered section on railing, and use wire to hang (if you like, conceal extra fabric by tucking it under railing). Gather bottom-left corner of fabric, and tack to railing with pushpin. Repeat with remaining corner. (If the swag is too wide, gather more fabric at corners, staple, and secure as above with wire.) Adjust folds to create billowing swag.