Another tip, pick a busy backing. I once machine quilted a huge quilt and thought I would put flannel on the back. Not a good idea since flannel has a habit of sticking to itself. Luckily it was a busy flannel because when I was done, there was a 6 inch wrinkle close to the centre. I wasn’t about to unpick it since the rest of the backing was good. I found matching thread and using an invisible ladder stitch, I stitched the wrinkle out. Even the quilt judge at our local fair couldn’t find it.