Lay down two intersecting chalk lines over the floor to divide it into four square sections, making the lines cross in the middle of the floor. After you snap the first line, but before you snap the second, set a carpentry square at the intersection to make sure the lines meet at a 90-degree angle.
Spread tile adhesive onto the middle of the floor, over the point where the lines cross, using a notched adhesive trowel. Cover enough of the floor to lay four of your ceramic tiles.
Press the first four tiles into place in the four corners where the lines cross in the middle of the floor. Put tile spacers between them as you lay them.
Spread additional adhesive and set additional tiles, working your way out along the lines while gradually building a grid pattern. Put spacers in place around each tile.
Tile the whole floor. Cut the tiles at the edges of the floor, by the wall, on a score-and-snap tile cutter to fit. Set the cut tiles with the cut sides facing the walls.
Allow the adhesive to set for a day. Remove the spacers.
Spread grout over the floor in sections of a few square feet at a time. Use a grout float to spread the grout, pressing it into the joints between the tiles. Use the long edge of the float to scrape the grout off the tile face. Wipe up the excess grout with a damp sponge. Let the grout dry for two or three days.