I am working on my accuracy. I find that right at the end of sewing a 1/4" seam, I tend to let the fabric slide a little bit off, usuallly to make the seam scantier. Maybe that is happening when you sew your blocks. Perhaps that is why your blocks don't line up, because that last 1/2" is where you are joining the block to another. I have become aware of this habit of mine to not be careful for the last little bit, and and I'm trying to improve in the accuracy department. The ironing thing is also something I never knew about, it was good to read about that.