Lay out your shirt and make sure the collar is flat. If your shirt needs ironing, do it at this time so there are no folds.
Mix the glitter with Mod Podge in a small dish. I would say a good ratio is 1:1.
Tape off the portion you are going to be Mod Podging and start applying your mixture. Let the first layer dry and then apply more in areas that aren't covered.
Repeat until the desired areas are covered and let dry completely before wearing.
Notes
The project is machine washable in cold water on the gentle cycle or by hand after 72 hours, and line dry.