hang in the centers of one side and then build up the first layer, after finishing that hang in the 4 adjusting centers and fill the spaces between them by putting in the edge pieces.
Now put the centers of the last layer in place (they fall to the side, don't care, they will get stable after putting in edges), now put in a few edge pieces to make the center stable and then finish the rest like at a 3x3.
It's not realy hard at all, I hope this small overview helps