Cut a strip of tartan that measures over twice your leg measurement where you will wear the tie. Remember to add enough material to the length of this strip to get the ends below the turn over of your hose. The strip should be wide enough to sew it into a "tube." Turn this "tube" inside out so that your seam is on the inside. At about 2-3" from the end, sew across the tube (i.e., perpendicular to the length) using a sewing machine zig-zag or double overcast stitch. Very carefully push this stitch up into the tube slightly, so that the tube wraps around it. flatten this out so that it does not bunch. Secure it with a machine straight stitch. Fringe the end as you would in making a kilt by pulling out threads.

Sorry these instructions aren't the best, I will be making a pair of these for my Black Watch kilt sometime tonight or tomorrow and I will take pictures and do a step-by-step.

As far as how they are tied, they are tied in the same way as the garter ties that Matt Newsome and the Tartan museum sell. Here is a link to their instruction page: http://giftshop.scottishtartans.org/garter_howto.html