I start cutting on the bottom left. My first cut is down the right side all the way through the bottom edge. I then cut across the top edge of the ruler all the way through the left edge. After moving that piece away slightly, I proceed to cut each one across that row. Next turn each piece around so you can cut the other two sides just like you'd be squaring up a piece. I have my ruler marked with the side I consider the top of the unit and always keep it up when cutting both times. Works slick for me.