Hey there quilt peeps....got a quick and useful tutorial to share.
Quilt Backing 101
Every quilt needs one and sometimes the perfect fabric is not available in a wide width. You know what comes next...wrestling with multiple yards of 44" wide fabric as you cut and sew it into the correct size and shape for your quilt. Often the ends don't match up and if you take your quilts to a professional for machine quilting that is often not their favorite thing to see.
I have a super easy method that yields great results that I would like to share with you.
Note: This is a fabric that is printed with two different prints on the same width of the fabric. Same color just a different print on each "half" - I share that with you so you will know that there are not 4 lengths to the back I am preparing but rather two.
First up is the long length of fabric - unfold it and lay it on the floor or wherever you have space. It's not necessary to press the center fold out at this point. The right side (pretty side) should be facing up.
Next up is to pick up one end of it and fold back on top of the fabric matching up cut ends. It will still be 44" wide but half as long. Right sides will be together.
You probably can't tell but the fold is now at the bottom of the photo and the cut ends are at the top. Selvages are on the left and right in this photo.
Next you take the cut end and match the two pieces as closely as you can. The folded edge should be at the opposite end (at your feet).
Take care to line up the selvage edges.
Set your stitch length to 1.5 and sew for about 1 to 2 inches. Switch back to 2.0 or even 2.5 to make it go quicker.
Remember that you will be trimming away the selvage edge so be sure to sew far enough away from it to allow for cutting that edge away. You don't want to leave that in your quilt.
Keep sewing until you get to about 2 inches from the folded edge - change your stitch length back to 1.5 and sew off the edge.
Now what you have is a perfectly aligned backing that is even at both ends.
Just a couple more steps...
Take the backing to your cutting table and with a ruler trim away the folded edge. You can see why you change your stitch length on both ends. I would go back and stay stitch across this cut end after I've pressed the seam to one side - yes to one side. If you press the seam open it leaves a weak area in the quilt and if you have a few popped stitches your batting will peek through.
Ta Dah! Quilt backing with just one seam where both edges are perfectly aligned and you didn't have to pin anything or wrestle multiple yards of fabric hoping it would turn out even and straight. Trim off the selvage edges next to the seam and press to one side. If you want to make your longarm quilter really happy go back and stay stitch the seam just and inch or so on either side of the seam along both edges so it does not pull apart as they load your quilt.
Hope this makes it easier to prepare a large backing for your next quilt.
Blessings,
Linda T.
PS: There is one disclaimer, this will not work if your fabric is directional because half will be going the right way and half the wrong way.
Keep sewing until you get to about 2 inches from the folded edge - change your stitch length back to 1.5 and sew off the edge.
Ta Dah! Quilt backing with just one seam where both edges are perfectly aligned and you didn't have to pin anything or wrestle multiple yards of fabric hoping it would turn out even and straight. Trim off the selvage edges next to the seam and press to one side. If you want to make your longarm quilter really happy go back and stay stitch the seam just and inch or so on either side of the seam along both edges so it does not pull apart as they load your quilt. 
