I find that a heat gun helps immensly, just blow hot air over the area you are glassing, don't get it so hot it bubbles, just very warm. After glassing, if you take Saran Wrap and place over the glassed area and smooth it out with your hands, let it cure overnight, and when you take the Saran Wrap off the next day, you will not even have to sand the result. It will be very smooth and slick.