The following information was provided by Manduka. These tips are for the Black Mat Pro, the Manduka Pro Mats, and the ProLite Mats which are all made of the same material but are different widths and thicknesses.
All new yoga mats have a thin film from the manufacturing process. There is a break-in period that everyone has to go through with a new mat before that thin film wears off and the slipping is almost completely eliminated. Typically, it takes about three months of daily practice and a "little" bit of slipping during that time so that the friction of feet and hands wears on the mat.
Once the mat is broken in, if you sweat a lot, there still might be a slight amount of slip in some standing poses and poses like down dog, but if you keep your awareness and energy moving towards, instead of away, from your center of gravity, the "slippage" stops and one can stay firm in the pose. Actually, a little slippage comes in handy on some poses, for instance shoulder stand or plow pose, when it's nice to allow the head to slide and the neck to lengthen.
Use it! Our customers have found that the best way to “break in” their mat is to use it on a daily basis.
Another trick is to leave it in the sunshine for an afternoon or sprinkle sea salt on the top surface of the mat, dampen with a cloth, and scrub it with a stiff scrub brush. (If following this trick, repeat this tactic 3 times, not just once, and you should see improvement.)
If you choose to do the Salt Scrub to help shorten the break-in period, alternate the scrubs with your practice. One day do the salt scrub, the next day or two practice on your mat, then do another salt scrub, and so on.
If you perspire sufficiently or are taking heated practices, please do consider using a Yoga Towel. These yoga mats are made of a closed-cell material that will not absorb any moisture or liquids. Perspiration, oils, lotions, etc will create a slippery layer on top of your mat causing you to slip. A Yoga Towel will absorb that moisture and allow you to practice safely and with more confidence.