I use the sandpaper dots on the back of all my rulers. This prevents them from slipping.
Probably cutting on the floor puts you at an odd angle which doesn't help.
Try cutting on a table so you can get a better angle at holding the ruler in place.
Hold the ruler with your hand, then hang your pinky off the edge of the ruler to keep it from sliding.

I use these, too, although I don't cut them up. I have tried the film but don't think it works as well as the dots.

When I use a long ruler such as the 4 by 36 " size, I use those large clamps (made out of plastic and with release lever on the inside handle). This ruler has a lip so it goes on the side closest to me and the clamp goes on the opposite side of the ruler. Works great. The clamps work well with some of my other rulers. They hold down the ruler and the cutting mat to the cutting table well. Depending on the size and shape of the ruler, I use one or two. The clamps are found in hardware stores, chain stores such as Lowes or Home Depot. A bit unorthodox, but it works for me.

Invisigrip the length and width of the ruler, "walk" your fingers up as you cut, and use one of the shower grip thingies as a handle. All those things help...but I still get it wrong! Good lighting also helps!!

I bought every gadget I could find to keep the ruler from slipping. I went to a class and the instructor led off with "don't let your ruler slip by running your rotary up above where your hand is anchoring" it. Dah. I am sure we all know that but I was always "zipping" my rotary up to the end of the ruler thinking I had enough pressure to keep from slipping. Now when I cut I go a little slower and adjust my hand on the ruler, what a difference.

I use the sandpaper dots. I also bought one of the suction handles they sell in Walgreens (the kind used to help you get out of the shower, etc) http://www.activeforever.com/p-26042...FQ84nAod-SAAPg

This is what I do. I also put the pinky finger of my left hand on the fabric to the left of the ruler to help stabilize it. And I use TrueGrips on my rulers. This seems to work for me.

Keeping your fingers spread and staying on your fingertips,and fingers slightly bent,close to edge of ruler and as you cut, move your fingers down, sort of like a spider walking,the ruler so they are parallel to your rotary cutter----I also keep my little finger off the ruler, but right up against it to insure that it won't move and get off the floor!

Love these!!!!!!!

The tip about keeping 2 fingers on the fabric is true. You will have to "walk" your fingers along the ruler as you cut; do not hold it in one place and cut way beyond where you are trying to cut. Try to cut shorter distances and walk your fingers along the ruler.