I attach the binding to my quilts by leaving a loose "tail" at the beginning and end, sewing around the entire quilt till I reach about 12 inches (30 cm) from where I started. Here's a simple diagram.
Now press the folds. Open both ends of the binding out so that the left side is facing right-side up and the right side is facing right-side down. Line up the pressed fold lines so that they form a + . Like this:
Pin the binding together and now sew diagonally through the + like this, keeping the loose ends of the binding to your right and the quilt to the left.
Once you have sewn the ends together, it's a good idea to check to make sure that you have sewn the diagonal correctly before cutting off the extra tails left over.
TA DA! it will fit every time. So now I have two quilts bound...just the label and hand stitching to do. Till the next time!!