Sorry if the pictures aren't great, it would have been clearer if I was using different coloured fabric in parts.
First of all, I take one of the two pieces I am joining and to the top of it I add a strip (gold fabric) right sides together that is an inch wide using an 1/4 inch seam. This strip will be part of the quilt top so you can either have it a contrasting fabric or one that blends.
At the same time as I sew this strip down the edge I sew another strip to the back. This one (brown fabric) is 1.5 inches wide and ironed wrong sides together along the length. A bit like binding. Sew with the raw edges of the strip along the edge of the quilted piece.
Once both strips are attached to the piece I pin the second quilted piece (the border) to the first part. I am only going to sew the border to the top one inch golden strip. I find it works best to have the piece with the strips attached on top so I can ensure that the back strip doesn't get caught up when sewing.
I stitch down this length again using a 1/4 inch seam which joins the two quilted pieces together.
When it is finished and you unfold it the front looks like this. The red fabric is the border that has just been added.
Now for the last bit on the back. Now you could be really good and hand sew this like you could for binding but I don't believe in that, far too much work! I've only done this a couple of times and am still experimenting with different methods but this time I decided to use a zigzag stitch. Because of the fold on the back strip you just sew down the edge.
Now obviously you may not like to see this stitching from the front but I don't mind. I'm treating it like decoration.
And because I am thinking of it as decoration, I wanted both sides of the strip with the zigzag and sew another line.
This picture shows where three quilted pieces are meeting.
From the front the red is the border just added. There was another border already added which is where the purple fabric starts. I am using different fabrics in my borders so the gold joining strip is visible, but if you were using all the same borders and the same for the joining strip it would be fairly hard to see.