Valley fold the top edge of the paper down to meet the lowest valley fold, this fold will bisect the fourth sixth from the top. Crease well, and unfold.
Bisect the fourth sixth by valley folding the top edge to meet the bottom valley fold. Crease well, and unfold.
Bisect the first and last sixths by valley folding the top edge to the closest valley fold, and the bottom edge similiarly. Crease well and unfold.
Rotate the paper 90 degrees, so that all the folds you made now run vertically through the paper.
Repeat the nine folds you made previously, which will nearly create a 12 by 12 grid, except that there will be four larger square in the center of the four quadrants of the paper.