Measure the length and width of the ceiling, using a measuring tape. Multiply the length by the width to determine the square footage and the number of tiles you'll need.
Snap a chalk line from one side to the other, using a T-square to ensure it is perpendicular with the wall. This line will serve as your guide.
Mix the thin-set mortar according to the instructions on the package. Use the notched trowel to spread a 1/4-inch layer of mortar that covers a space several tiles wide.
Lay the first tile, using the chalk line as a guide and pushing upward firmly, with a slight twist to ensure the tile is set securely.
Add spacers on all sides of the tile. Continue setting the tiles until you have finished the first row.
Cut any tiles on the ends that may not fit, using a tile cutter. Use tile nippers if you need to cut curves into the tiles to fit around ceiling fixtures. Allow the thin-set mortar to cure overnight.
Remove the spacers from between the tiles.
Mix grout according to instructions on the package. Use the rubber trowel to spread the grout in the spaces between the tiles. Wipe away any excess grout from the tiles with a damp sponge.