Below is a comment I made in the 1.5" swap thread. I use 1/4" seams and starch, even when using 3/4" cuts for 1/4" finished pieces.
"I think the first order on the small stuff is to have accurate cuts, then sew an accurate, consistent seam.
One thing one has to watch is how you start and end the seam. I call it the l-r swing. We as sewers tend to start to far to the left, curve into the 1/4" seam allowance and then end up too far from the right making a slight "S" shape in the seam. Try sewing 2 1.5" squares together with highly contrasting thread and see if that's a problem for you. If it is true for you, simply try to start and end straight. I catch myself doing the l-r swing everyonce in while and usually go back and resew the seam correctly.
I don't press open, I get a better match by pressing to the side and butting the two seams together or "locking them in place" as Eleanor Burns would tell you."