The first fun part is decorating your background paper. Paint, draw, spray, decoupage your heart out.
I have many pieces of watercolour art and decided to use a piece from my (in)famous watercolour graveyard.
As you will see, I sectioned the paper into 1" strips. I used a pencil to draw moderate weight lines and then went over the lines with a Conte a Paris white pastel pencil. Smudged it a little. I love the way it defines the borders of the squares.