I use the
Sew Steady Slider Mat -- I purchased a couple after I found out I liked it for ruler quilting and I'm still using the same one three years later doing free motion and ruler quilting. I haven't even opened the second one yet.
I rinse it off with water to get the fuzzies off the back, if there are any after I'm done with my entire quilt and then put it away for next time.
An added note: using quilting gloves also is a big help when you are ruler or free motion quilting. I use these:
Machingers Quilting Gloves