One tip I learned (almost too late) is to begin quilting on the quilt sandwich in the center and sew with a walking foot to the edge; THEN, return to the center and sew out to another edge; repeat returning to the center for the last two edges. Then I keep smoothing and work within the quarter sections using a FMQ foot with dogs down. This has eliminated puckers for me (I spray baste, though, and pin where it seems necessary using quilting safety pins).