Silver Needle has done a much better job of describing the technique that makes excellent corners.
I use a 3/8" seam allowance when attaching the binding. When I get about 4" from the corner, I measure up 3/8" from the end and mark it with a pin perpendicular to the end. I slowly approach the pin and stop right when I get there and then backstitch. It works every time for me.
Dayle