Begin with 6 strands of yarn, split these into 2 sets of 3.

Take the set on the left and form a loop over the top of the set on the right.

Take the set on the right and pass it over the top of the bottom part of the set on the left and then underneath the top part of the set on the left.

Pinch the part of the right set where it crosses underneath the loop made by the left set and pass the end of the right set underneath this part, but on top of the loop.

Now take the two sets and pull on the ends to tighten the knot.