Measure the width of the tile and divide it by two. That will give you the center of the tile. Place the center of the tile at the wall’s center mark. Then mark the wall at each end of the tile. Repeat this process on the three remaining walls and then snap chalk lines from the marks to those on the parallel wall across the room. These four lines will create a cross hair at the center of the room.
Place the first carpet square in center of the cross hair and work tiles out from that center point. If the carpet squares have an adhesive backing, do not remove the cover from the backing yet. In the photograph chalk lines are highlighted with painter's tape to demonstrate the crossing lines used to center the first square.
The last step is to cut the carpet squares to fit at the wall. Turn the carpet square upside down and set it flush with the wall and mark at both ends where the carpet square overlaps the next to the last rows of full carpet squares. Use a carpenter’s square or straight edge and a utility knife to make a straight clean cut on the backside of the carpet square. Install the partial square with the cut edge against the baseboard (molding will cover it if it is not exactly even).