I measure carefully through the center of the quilt. I usually check as I'm putting the top together to make sure both sides are even. Cutting is either lengthwise or crosswise depending on the fabric. I mark the middle and quarter points of both the top and the border. Then I pin pin pin matching the middle and quarter points. I usually sew with the border on the bottom so I can make sure my block seams aren't twisted. Putting on borders is my least favorite part of quilting but mine always lie flat.