Measure the length of your mantel, and multiply by 1 1/4; cut ribbon to that length.
Using a ruler and a pencil, mark ribbon at regular intervals. (We marked the ribbon every 6 inches for the larger garland.)
To create swags, mark a second ribbon at regular intervals, with spaces at least an inch greater than that of the first ribbon; leave several extra inches on ends. Make creases on second ribbon wherever marked.
Apply hot glue to top of first crease, and attach it to the first ribbon where marked, holding crease at a 45-degree angle across width of first ribbon; hold in place just until glue sets. Repeat. (For additional swags, repeat step 4 with more ribbon, and use hot glue to attach swags at creases.)