I purchased a package of fat quarters awhile back and have just gotten around to unfolding and appreciating the selection of fabrics. As you can see in the photo, creases are quite noticeable. Since it will be a few weeks before I begin a project with these fabrics--and I don't want to shelve them creased, I opted to roll the fabrics to begin the process of relaxing the weave without having to iron each fat quarter.
Smooth a fat quarter on the table, then add and smooth each fabric on top. Start the roll on one side that is parallel to the selvage, and hold the roll up to continue rolling. The process will render the fabric layers uneven--outer layers of fabric will take more surface to travel the outer circumference of the roll. Holding the roll up allows the layers to fall and correct themselves.
Much of the creasing will relax--ready to lightly press when it's time to begin your sewing project.