Before turning your mat over and using the other side, check first to be sure the reverse side is meant for cutting. Not all brands have a cutting surface on the back.
Also, in addition to the other tips mentioned for caring for your mat ... I use a mat smoothing stone to clean my mats after every project. And make sure the blade screw is tight on your rotary cutter, if you have that kind. A slightly loose blade will cut small grooves in your mat, just like a dull blade will.
Good luck!