Read your copy out loud. It's the most effective way to spot any glitches. Does your copy appeal to the ear as well as the eye? If your copy doesn't flow smoothly, it needs to be re,written. Good sales copy doesn't draw attention to itself; it merely resonates with the reader and engages his senses. Any potential stumbling block needs to be removed. Anything that causes the reader to pause because the meaning wasn't absolutely clear, gives the reader a reason to move on.