We are often asked to line up quilt tops to the patchwork on a quilt back. I thought to share this tip when I answered a query on Facebook today. It was too good to not pass along further.
In addition to the side to side alignment, you can do one more step to improve alignment. If you have seam junctions or other requested features to match front to back, use long pins to stick up through to the top, from under the quilt as it is pinned up to your rollers, then replace the pins sticking up with pins to secure that matching point from the top.