Don't laugh but I've see folks use the rotary blade on the outside facing away from the edge of the ruler instead of being directly next to the ruler.
Also cut away from your body, not toward.
Cut about 8", stop without lifting blade, let your hand holding the ruler 'crawl' up a few inches, then cut some more. It's hard to describe without showing you but you need to shift your weight on the ruler as well as the cutter.