Spiral Knot aka Half Knot

A Half knot (or Spiral knot) is the first half of a Square knot.  If you tie several in a row, they naturally begin to twist and you get a spiral effect.

Place the left cord over the filler (or holding) cords (the one, or more than one, in the center you are tying onto) then put the right cord over top of the left.

Slide the right cord under the filler cords then out and over the left cord.
Tighten it up.  Then take the left cord again and put it over the filler cords.  Lay the right cord over the left.
Thread the right cord behind the filler cords, then out and over the left cord.

As you continue on tying from the left the spiral will look like this.

If you were to tie knots from only the right side, your spiral would twist differently and look like this: