If possible, don't cut through too many layers. My cuts are more accurate when I don't cut through more than 4 layers, preferably only 2 layers. I'm waiting until I master the accuracy aspect before I worry about being more efficient or fast. If all the layers aren't folded perfectly, the folded areas will come out wonky. Measuring with the ruler instead of the mat seems to work better for me. Also, I've had better cutting results when I starch the fabric during ironing, especially since I pre-wash.