Nesting the seams and pinning help alot. Even if your seams are good, sometimes it doesn't match up because fabrics can stretch a little. So one might stretch a lot and another not much. Pinning really helps. I slow down as I get to the pin and take it out at the last minute. If necessary, I give a little tug while sewing to compensate for one being a little off. if the whole row is larger than another, put that row on the bottom when you sew.