I'm currently making log cabin blocks using QAYG and find that starching and pressing are a good place to start. When I attach each strip on, I measure the distance across the top and bottom of the square after I've laid the next strip to be sewn on. That uses the straight edge on the left as the reference point rather than the pieces on the right that you are sewing over. It only takes a thread or two off to make the block look wonky and this method works for me to keep it acceptably square. Fabric is such a flexible medium to work with that there is almost always something to ease or trim. Part of the craft of quilting!