Measure the center points of the room in each direction. Snap a chalk line along each of these centers. At this point, the floor has two lines intersecting at the center of the room.
Start the first row of tile at the center point. Place the first tile with a corner at the point of the intersection and continue with tiles along the same side of the first centerline.
Start the second row with the first tile centered over the second line. Place the tiles against the tile of the first row. The seams of the tiles should be at the midpoint between the tiles of the previous row.
Place a third row of tiles on the opposite side of the first row. Center a tile over the second chalk line in the same manner as the second row of tiles.
Continue adding tiles on each side of the rows of tiles in the center of the room. Alternate rows starting with a tile edge adjacent to the chalk line and centered on the chalk line. Continue the process until the entire room is tiled.