(Please note: Pink lines connote how the paper is to be folded, and black lines connote previously folded creases, as well as the edges of the paper.)
Cut a piece of paper that is square and between 12" and 13" on a side.
Fold corners to opposite corners and open.
Fold top to bottom, open. Fold left to right, open.
Fold all four corners to center point, open.
Fold A to B from behind (C will pop up off table). Fold C to D.
Fold C-D, E, and F to center.