Measure tabletop, add 12' for total overhang. Purchase material in desired width and length. Hem edges by sewing, using iron on seam tape or gluing with craft or hot glue.
First measure your table and determine how long you need the runner to be. If you can sew by hand or use fabric glue. Go to the fabric store pick the fabric then simply make a 1/2 inch fold under the fabric and stitch or glue it in place.
If you are a weaver, you can make a table runner on a loom. If not, buy the appropriate length of fabric, cut to fit the size you need and hem all edges. You can make one of a plain fabric and embellish with hand painted objects or stencils.
To make a table runner you would need to decide the size and width. Purchase some cloth and have a sewing maching for that you can stitch everything together.
Prewash fabric and press it.
Use a fabric-cutting board, yardstick, and fabric-marking pen to measure out a length of fabric
Make a mark at the center of each short edge.
Pin table runner front to backing piece.
Stitch around the edges