All of the hints everyone has given you are great. Sometimes when I am trying to match corners or whatever where I want it to be perfect, I do my best pinning tricks and then just sew 4 or 5 stitches across the intersection instead of the entire seam. Then I open it up to check it. As you said sometimes even with our best pinning, the blocks still shift. This way if it has shifted I only have those 4 or 5 stitches to remove. If it's perfect when I check, then I go back and sew up the rest of the seam. This is a trick I was taught back in the days of making our own clothes, but it surely helps in quilting too.