If you like, you can lay a flat ribbon or other straight, bendable object over the shirt to keep track of where the line is.
Don’t worry too much about finding the exact middle of the line, especially before you’ve got the hang of this. You do not need to measure it exactly to end up with a tidy, folded shirt.
Again, make sure to pinch both the front and back fabric. Since this is at the end of the shirt, it should be easy to place the shirt between your finger and thumb.
Your right hand should move directly over your left in a straight line, and continue to the bottom of the shirt. This motion follows the imaginary line.
This is the easiest part of the fold to mess up. However, once you’ve understood the type of motion you need to make, it will be easy and quick.
If the loose sleeve isn’t completely hidden after you lower the shirt, it’s easy to tuck the sleeve under the shirt by hand.