Remove any spacers used in your tile installation. Inspect each grout joint and scrape out excess mortar from the tile application. As you go, clean the joints with mineral spirits to remove surface dirt and dust.
Wipe down the entire tile surface with a rag dampened in mineral spirits to remove any contaminants on the surface that could ruin the way the grout bonds to the joints. Allow the tile to dry completely, or wipe it dry with a clean towel, before continuing.
Moisten the grout joints and the tile surface slightly with a sponge dampened in clean water before starting. This will help you spread the premixed grout around.
Fill a rubber grout float with the premixed grout directly from the bucket. Spread it across the tile surface and into the grout joints with a diagonal motion of the float. Ensure that each joint is completely filled and packed down tight with grout.
Scrape the clean edge of the float diagonally back across the surface to remove most of the excess grout from the surface. When the joints are all filled in, they will be flush with the edges of the tiles. Fill in all joints and allow the grout to set for 30 minutes before continuing.
Run a cellulose sponge diagonally across the tile surfaces to remove any grout residue. Rinse the sponge in clean water after each pass to remove excess grout. Continue until all excess grout is removed. Allow the grout to dry overnight before exposing the surface to any moisture.