Originally Posted by Prism99

If you just sew a border strip on without measuring and pinning first, you almost always get that ruffle effect. Too much border gets sewn onto the edge.

To solve the problem, measure through the middle of the quilt and cut the border to that length. Fold both the quilt and the border into halves and quarters, and pin generously matching edges, centers, quarters, etc. Only then do you sew, easing the quilt edge if necessary to fit the border.

As someone else mentioned, it's a good idea to sew with the border piece next to the feed dogs to lessen the tendency of the border piece to stretch. It also helps to heavily starch the border piece (before cutting, if possible) as this stabilizes the border so it doesn't stretch while sewing.