All these suggestions are great. I also start by cutting the border piece to fit the center measurement. Then I mark the mathmatical center of the border strip. I then find the center of the quilt top by design (I hope that makes sense) I pin the top and bottom of the quilt to border and then pin the two centers. I then ease the quilt top onto the border strip and sew.
Note - If you piecing is accurate, there should be no differenct between the mathmatical center and the design center, but hey - you never know. Fabric is a living thing!