It's a great idea to add a hanging sleeve to the back of your quilt -- especially if they are wall hangings.
First, measure the top of your quilt.
Second, cut the sleeve fabric width, 9" for a large quilt or 6" for a small quilt. Then cut the length 1" shorter than what your quilt top measured. Fold the sleeve with right sides together. Then sew both ends,
back-stitching at the beginning and end. Trim the corners and turn
Center the sleeve on the back of the quilt and pin in place. Then baste it in place. Sew the binding to the front of the quilt, catching the sleeve in the seam as you go. Finish binding the quilt, sewing through the sleeve on the back as you go.
Create some fullness at the top of the sleeve by folding it just below the top edge of the binding. Pin the bottom edge in place.
Sew the bottom in place by hand. I use a blind stitch.
Here's the finished hanging sleeve.