Use a capped pen, a coffee stir, a chopstick – anything that points. Because the design is woven, you can cross over the lines. Because the design is endless, you can start anywhere and stop at any time.
Tracing isolates the hand-to-eye coordination. This forces the mind to focus. When the mind can focus, it can calm down - and so can the nervous system
In short, once you begin tracing you begin meditating.