Take a square scarf
 fold corners towards the center
 then, fold the scarf in half
 make a loose ponytail at the lower back of your head – top of your neck
 wrap folded scarf around your head and tie a knot under the ponytail
 then use one loose end of the scarf and wrap it around the ponytail making another knot on a side. You could chose to tuck in the leftover scarf or not.
This is a very simple way and what I like about it, is again, the messy, natural look you’re getting.