This is my technique for layering a finished quilt. I found that trying to get all the layers to lie flat for pinning and/or basting was difficult. I've made many quilts and have found this to be the best technique for keeping all the layers flat and taut for machine or hand quilting.
Step 1: Lay Out Backing Fabric
After sewing together your backing fabric, lay it down on a flat surface (right side down). I used to use my dining room floor because it was the flat surface in my house that was large enough. When we put in a new tile floor in my laundry room, I found an additional surface that works. Make sure the fabric is square with the floor. The tile blocks work well for this as do the lines on a hardwood floor.