I love observing patterns around the house. I noticed this one of the sunlight on my studio window. When I turned it horizontally, I noticed the "squiggly lines" that are seen in many designs.
I took the left side of the image into Photoshop Elements. I chose a small brush from the calligraphy brush set. The calligraphy brushes have a hard edge and the brushstrokes can be created with a thin, angled edge that goes into a wide one.