Measure to the midpoint on two opposite walls and draw a line down the center of the room. Find the midpoint of this line and draw a line perpendicular to it, leaving you with a cross on the floor that divides the floor into four equal sections.
Draw two more lines that are at 45 degree angles to the first two, leaving you with four lines that meet at the center of the room, dividing the floor into eight equal pie-shaped pieces.
Spread mastic on the floor. Only spread as much as you can cover with pieces of wood within half an hour or so, otherwise the mastic will begin to harden.
Place the first piece of wood at the center of the room with one of its edges running along one of the diagonal lines. Tap it down into the mastic with a rubber mallet.
Place a second piece of wood perpendicular to the first piece so that the two pieces form an L. Be sure that their tongues and grooves are firmly meshed.
Work out from these two pieces with other pieces in the same pattern, checking frequently to be sure that the orientation of the pieces is at a 45 degree angle to the walls of the room.
Trim the final pieces of wood with a chop saw to fit into the remaining spaces when you reach the walls of the room.