I do this by "feel" I put the fabric together with the seems going in opposite directions and I use my thumb and forefinger to "slide" them into place. Then I pin on both sides and sew. I do not take out the pins until the entire seam has been sewn.
For foundation piecing with many point that have to be perfect, I baste each point on the machine with a long stitch (on my machine a 3.5) and I sew just where the points will meet. Then I open it up to see if I did a good job, If not I take out the basting and do it again. If it makes me happy I just sew over the basting stitches when I sew the 2 pieces all the way.
My best friend says I am way to picky, her train of thought is if you cant see it driving by at 60 mph it is not a problem LOL