I'm fairly new at this, so some of the experts may do it another way. But, here's how I do it: I use my 24"x6" ruler and my cutting mat. I line up the edge of my folded fabric on the 1" line on the mat (with the 1" line to my right. If I'm going to cut a 9" strip, I line up my ruler with the 10" line at the top and bottom of the mat. Then I cut. Voila, I have a strip 9" by WOF.
I sure hope this makes sense. I'll stand by to see what the experts say.