Trim away the excess batting, leaving about 3/4" of batting beyond the edge of the quilt top. Trim the backing about 3/4" away from the edge of the batting.
Fold the backing over the batting. Butt the raw edges of the 2 fabrics together. Baste the backing over the batting. Do this on all four sides of your basted quilt.
You'll be surprised at how much this simple step will protect the outer edges of your quilt from stretching and fraying as you work. And it cuts down on the amount of lint generated when you machine quilt.