Barb, the last quilt I made I was going to use a 2 1/2 strip for binding, but the material was a little to thick, so I used a 3 inch strip for binding. I use my walking foot and the side of the foot for a guide. which makes the seam a little more than 1/4 inch, but I don't care as long as I am consistent. I don't like a real thin binding. Nor 1/4 inch seams. lol. Once the binding is on, it is measures just about 1/2 inch wide.
I make sure the edges of the quilt are even. Sew the binding on the back. If you put your binding on the top of the quilt when sewing, it is easier to miter the corners.
Once the back binding is on I start folding and pinning the corners, pinning about an inch down from the corner and pinning along the seam. I use my long needle as a stiletto to push the bottom material of the miter way up in the corner and fold the top down to make a perfect corner and pin it down. Three pins to a corner.
I start sewing in the middle of the quilt, leaving about 6 inches of binding for matching up . I fold the binding over and insert the needle where I want the top seam to be and point it down to the back seam and sew towards the needle. You should be sewing right on the back seam, or in the ditch. Hopes this helps.