In this case I also cut the fabric on the bias to get the diagonal effect that matches a section in the needlepoint piece.
I would not recommend that a beginner does this as the bias edges stretch which can cause problems.
This helps even out any unevenness in the piece due to embellishments etc.
First I pinned the hem to the edge of the needlepoint.
It works really nicely and pulls everything together.
For more info on ladder stitch try this link.
I know that online these cubes have fancy bows on top, I tryed one and it was just too fussy for my taste.