I have always told my students to cut and square up their batting and backing to match the same size as the quilt top. They cut their binding pieces 2 1/2" wide and make enough for the entire quilt. I usually suggest 8-9 strips 2 1/2" x 45". I show them how to attach the binding so the raw edges of the folded binding are matched with the raw edge of the quilt. Pin the entire binding in place, make their mitered corners and finish off. I have them sew their binding approximately 1/4" from the edge of the quilt (or the width of their quilting foot as it is much easier to sew the binding down with the quilting foot.
I hope this helps. pin pin pin!!!!!!!! that's a big key!
Cheers
Andrea