It is so much easier to show this process "in person", so bare with me. I chose a stripe that is not the same from either direction and cut four 3" x wof strips. For the body of my sample I cut a 36" square. This can be done with rectangles as well, but it will be easier for you to try the first time with a square. I'm also using a marker for the 1/4" dot markings which I would not do on an actual piece.
This is simply "fussy cutting" the mitered borders. Seem like it takes a good bit to cut them, but it actually goes quickly and sewing is sooooooooo much faster. So here goes:
Cut four strips 3" x wof. stack them right side up, wrong side up, right side, etc... matching and pinning the stripes exactly together.
Pin strips together being careful to match stripes as accurately as possible. Cut a 45 degree angle beginning near the selvage.
After making the cut, leave the pieces pinned together.
Since we know the piece measures 36" across the center, subtract 1/2" from that to determine the length of the short side of the border. Meauring from the top corner of the cut 35 1/2" to determine the top corner of the cut on the opposite end.
This picture shows better the entire strip that measures 35 1/2" from one top point to the other.
mark the spot that would be 1/4" from the end of the seam. In this case it is where my two lines cross. Mark the 1/4" dot on the body of the piece, also.
Pin the 1/4" dot or interstions together, pinning the two ends first.
After pinning the two ends accurately, carefully pin the edges together.
Sew a 1/4" seam starting 1/4" from the end on the dot and ending at the 1/4" mark or intersection. Be sure to backstitch to secure stitching and sew as accurately as possible.
To add the next border in a clockwise direction, fold back the 1st border to reveal the 1/4" dot. Pin the next border in your stack,matching and pinning the dots then the rest of the border. Stitch dot to dot as before being careful not to catch the 1st border in your sewing.
Accurately pin the dot and sew dot to dot with backstitching at each end.
Stitching doesn't look straight but you get the idea. On the other side the stitching should come right together at the 1/4" from the edges.
fold the edges back allowing the mitered borders to extend beyond the corner.
Sew a 1/4" seam starting 1/4" from the end on the dot and ending at the edge-backstitch.
Seam before pressing open.
This picture shows two corners matched. The other two will be just like these.