As you thread your needle throughout the neckline, be sure to pull the thread completely through each hole that you make. Repeat this process around the neckline until you reach your starting point.

To tighten the neckline, hold down on the shirt itself as you go along and pull on the needle-end of the thread. This will cause the fabric of the shirt to bunch up.

You want the fabric to bunch up only slightly, otherwise it'll be too tight for you to stick your head through. Try to find a good balance!