I use a 6.5 x 24.5 inch ruler. I have clear rubber dots on each corner of the ruler and one mid-way down on each side. Also, I have found that if I re-straighten the cut side of the fabric every 3 or 4 strips, I don't get the curves and v's. Also, I try not to have more than 1 fold in the fabric. I have friends who will fold their fabric 2, 3 times and cut. When I have done this, the thickness causes problems and my ruler can move off like more easily. So I try not to do this unless I really have to.