Originally Posted by Iceblossom

I don't know if it will help you, but what I've found is to make an L shape with my sashing on my squares first, then you put those together. It works much better than trying to accurately set on a long unwieldy skinny length to a wider length. Once you have all the L shapes on, then layout the quilt (if you haven't before) and put on the extra top and side pieces.

In general you just get better results when you put similar sized pieces together.

I also press my seams open, so typically matching seams isn't an issue for me.