Fold your scarf into a triangle

then fold the long edge over, about 5 inches wide

gather the ends together

and bring behind your neck

cross the ends..

pull tighter..

.. and bring them forward

From here, you can proceed in a variety of ways. You can simply tie the ends into a double knot, or use a scarf ring (moyenne size) to secure them in the basic slide or criss-cross method.
Scarf ring sizing info:
MaiTai Collection Moyenne ring: perfect for 70 Carrés and PM Mousses
MaiTai Collection Grande ring: perfect for 90 Carrés and GM Mousses