Get ahead of the game by shaking off excess glitter before you wear your shirt. Place the shirt into a mesh laundry bag and put it into the dryer for a few minutes. The agitating action of the dryer will help shake off glitter so it doesn't come off while you are wearing it. Tumble the shirt without other clothing in the dryer, unless you want to get glitter over your other clothes.
Right before you wear your glitter shirt, mist it lightly with hairspray. Use an aerosol hairspray for the best results. A misting of hairspray helps glitter that might otherwise fall off stick to the shirt instead. Make your hairspray do double duty when you want to rock that glittery shirt.
Remove spots and stains gently. If your glitter shirt is machine washable, use a spot treatment and a sponge to lightly dab at stains before washing. When you are ready to wash, turn the shirt inside out to protect the glitter during the wash cycle. Better yet, try washing the garment gently by hand to preserve your glittery goodness.
Dry that glitter garment carefully after you've washed it. Hang it onto a hanger and use a blow dryer to allow any falling glitter to release. You can also use a mesh laundry bag in the dryer for a few minutes to shake the garment free of wayward glitter.