My method is not the easiest, but it is the preferred, at least for me. If the directions say cut a square to the 8th of an inch I cut to the next quarter, draw a line diagonally down the center, sew 1/4" on either side, cut on drawn line, press open, then square up to desired unfinished size. It will take a lot of time if you have dozens to make but the finished product is perfect and all are uniform and the intersections are much better (& less frustrating!). If no pattern then cut squares 1 inch larger than finished size. When making lots of HSTs, say you need 8 HSTs that finish at 3 inches then put two 8" squares RST, draw diagonal lines from corner to corner, sew 1/4" on either side then cut the squares in half horizontially and vertically then on the drawn lines. (Writing directions is hard)
By the way, I have the Wonder Ruler and have not used it since right after buying it. Maybe it was me but my squares just weren't uniform. Now I just use a standard ruler to square up.