Cover your furniture with drop cloths. Combine 1/3 cup trisodium phosphate with 1 gallon of water in a bucket. Dip a mop in the mixture and swab down the ceiling completely, allowing it to air-dry.
Put on a hat and protective goggles. Apply paint to the ceiling in 3-foot by 3-foot sections, using a brush or trowel.
Load the glitter into the glitter gun. Step on a stool or ladder just underneath the freshly painted area.
Aim the glitter gun at the wet paint and spray it with a light mist of glitter. Examine your work. If you'd like a thicker coat of glitter, repeat.
Continue this process until you cover the entire ceiling with a light hint of glittery sparkle.