I always rip on the straight of the grain. I measure a little wider than called for so that after I have ripped the strip, I can fold it as many times as needed to get a managable length that I have a ruler long enough for, remeasure and then cut on each side to get rid of the ravellies. I hate them and want a nice straight clean edge. Ripping always seems to come out straight and is a good way to make sure the edges of the fabric are straight too! This may go against the grain for some folks since it does 'waste' a little bit, but I don't mind 'wasting' some to get what I want.