One thing I do is when I sew the corners, is a 45 degree stitch. As I approach within one or two stitches of the quarter inch I turn the quilt 45 degrees and take one or two stitches across the corner. If the batting is thin, one stitch, if the batting is thicker, then two stitches. This gives a little ease in the corner and makes a sharper turn. I test the corner by turning the facings to the right side and will sometimes trim just the tip off the quilt corners to remove excessive bulk. Beware to not trim to deep or the corner gets soft and will not hold a good shape.
Do you have a favorite finishing technique?