After watching many experts methods I use this one.
When you reach the 1/4 inch from the corner angle towards the corner and back stitch off the quilt. Dont take quilt out of machine just pull it out far enought to fold the corner over even with the top of quilt then stitch down that side. If neccessary mark the 1/4 in or put in a pin to be sure you are at the 1/4 inch from edge.
The fold should be even with the edge of the top of quilt and even with the folds under the left side of binding.
It really is simple but sure hard to explain.
I like Sewing with Nancy and El Burns methods best.