You could draw lines on the foundation first, to help you be sure the center section is covered with selvages.
Then add selvages to the corners. Trim. I rounded the corners of the finished square so that the pillow wouldn't have little pointy things on the corners.
You may remember that I made this pillow for the Moda Bake Shop, and it was featured in a give-away a while back. This piece is unusual in that the selvages are so coordinated.
If you would like more directions for selvage quilting, visit www.selvagequilts.com and click on Workshops. It's all free; you can use anything you find there for classes or whatever you want.