Love this tip from American Patchwork Quilting.
Was reading my new magazine the other day and a tip was to use the nonslip shelve liners ( they cut one out of a heart in the pic) and put under your ruler to stop the slipping. Well okay I didn't cut out of a heart, but I did cut a 2x3 rectangle and a 1.5 x 3 rectangle and gave it a try. No more of those little sandpaper dots on my rulers. This is amazing. I wish I would have thought of this long time ago.
One thing I do use though is painters tape, cut off a small piece, roll it so it's sticky all around and then put it either under fabric, but mostly use when I'm making stencils out of plastic. It really holds the fabric too.