Spray basting helps a lot to prevent puckers. Heavy starching also helps. I always use a heavy starch solution on the backing fabric before layering (1:1 solution of Sta-Flo and water), and also use spray starch on the top. Starch stabilizes the fabric to prevent it from distorting while you handle it.
You might want to try wavy lines using a walking foot. This is a really easy way to machine quilt with no worries about stitch length or staying exactly on a line or in a ditch. You can even do wavy lines in both directions to create wavy cross-hatching. Try it on a large practice sandwich; you might like it!