I sprayed basting spray on the back of my ruler, then rubbed most of it off. It now 'grips' the fabric, so the fabric doesn't slide. Because my hands don't like holding the ruler in place, I place my forearm (elbow to wrist) about 4 inches in on the ruler. It works for me, but is probably not a the safest way to cut, as the blade does slip on occasion. I started using this method, though, the second time the blade got away from me and nearly cut off the tip of my thumb.
Again, my method of keeping the ruler in place is probably not the safest way to do it. I did try the little sticky dots, but the ruler slipped anyway. The clear double sticky tape does sound like it would work very nicely, though.