rvsfan....I usually try to use the same fabric as the front so that if you don't get it exactly right, it doesn't show as much.
The most comprehensive instructions I have found for facing a quilt are these from Blue Moon River. They cover how to stay stitch through the facing and seam allowance, which gives you the absolute best knife edge. I use it on all my show quilts. It is an extra step but will gives you great results. I think it is step #8 in their instructions.
Facing instructions
Watson