Measure ALL of your squares first. Take the smallest/shortest one and place your ruler on top. Make sure your block is laying flat and smooth. Line up the 45* line from corner to opposite corner. Middle of this line laying dead center on block. Trim away fabric outside of ruler edge with your rotary cutter. Turn block clockwise, do all over again until all sides are done. From the smallest one now you can trim the rest. However, if you have points that may be trimmed away, that is a whole 'nuther story.