When you sandwich a quilt, the back should be nice and taut, but not stretched. You can use masking tape to hold it down, or straight pins if you are on a carpeted surface. (You really should press it too. Really.) The batting, if it came packaged, should be tossed in the dryer, at the very least. I like to pre-wash mine (soak, spin, no agitation) then dry. It takes out wrinkles, pre-shrinks the batting, and makes it much easier to lay out over the backing layer. Smooth it out completely, eliminating all folds, creases, and air bubbles. Finally, make sure your top is pressed (yes, really. I promise it won't hurt you) lay the quilt top on the top of the batting layer, making sure that it isn't upside down if you have a directional back. Smooth out all wrinkles, folds, creases, air bubbles. Most folds in quilting occur from less than perfectly constructed tops, and/or less than perfect layering of the quilt. Ask me how I know. 😀 I have learned everything the hard way.