I have recently purchased a quarter inch pressure foot. This has worked wonders in helping me to match seams (still nest, pin etc) and my blocks come out to the size they are supposed to be ..... IF I cut accurately to being with.
I also use Washable Elmer's Glue to match up seams if it is a stubborn seam. This allows you to glue, press to set, and open up to see if it matches. It can be repositioned if necessary.
I have recently started sewing just over the seam to make sure it matches before sewing the entire seam. Saves time in rippin' if it doesn't match.