Here are some tips that I have deducted from many practices: When you "pinch" the shirt, do not pinch it so tightly (as GQ Lawyer has noted). The position you pinch the shirt and the line that it relates to at the top seam is the most important part. Pinching higher (closer to armpit) allows you to stretch the shirt farther when folding it over your arm, thus creating a tighter rectangle. To make the fold symmetrical, grab the top seam closer to the collar than to the shoulder. If you have more space on the right side, you are pulling from too close to the shoulder. If you have more space on the left side, you are pulling to close to the collar. Many hours at the office have been killed by practicing this.