buy a june tailor strip ruler... it has slits every half inch so that you fold straight and WELL and then place the bottom black line on the near fold....now every half inch, you have an opportunity to slice thru the 4 layers of fabric with no ruler movement at all... then move those strips, line up the '0' line with the new raw edge and work away again...the standard is 12" wide and so you have multiple slits before you have to move the ruler. Now either lay one strip (still folded) down, line up the bottom black line again and repeat across to get squares....or much better still.... sew the strips together first....THEN, fold the new 'striped fabric' you just created and put the ruler on it...now when you slice it, you will have your squares all sewn in a long line with less than half the work...learn to line up a straight line with the bottom black line before cutting and you will have perfect squares every time...