I empathize with you. Cutting straight is also a challenge to me. Placing little dots of sandpaper or true grips or a similar product to the bottom side of the ruler will help keep it from sliding, which is often where the crooked cuts arise. Also, the markings on the ruler aren't always easy to see. If you place a piece of blue paimter's tape on the line you will be using, it can help. Good luck.