Originally Posted by Prism99

Are you machine quilting on a domestic sewing machine? If so, I recommend *heavily* starching the backing fabric (or the backing, if already sewn together) before sandwiching. Starch stabilizes the backing so it is much less likely to pucker or fold over on itself while quilting. My method is to use a 1:1 solution of Sta-Flo liquid laundry starch and water, "paint" this solution onto the yardage using a large wall painting brush until fabric is saturated, wait a couple of minutes to make sure the starch has penetrated the fibers, toss in dryer, and iron with steam. I also spray starch the top before sandwiching, to help stabilize the top.

Finally, I recommend spray basting instead of pinning. I actually ruined an expensive walking foot when it got caught on a safety pin I had missed taking out. Spray basting is better than pinning because all 3 layers of the sandwich are connected continuously; with pins the layers are connected only at the pins, and layers are more likely to shift.

If you do pin, then a rule-of-thumb is to have a pin every 4 inches in every direction -- about a fist width apart from each other.