First, make a pattern on light card stock. Cut it out making sure it's symmetrical. Trace it onto the back of a piece of white fleece. Then, trace the line with a small amount of Tacky Glue.
Lay a piece of flexible cording (I have used a yarn cording) onto the glue:
I have just listed a batch of new embroidered saddle pads, available in my Etsy store: