You can try different picks that have texture to the upper part for grip and see if that helps. I really believe though that most problems with pick grip come from holding it incorrectly. Regardless of how you hold it, you need to make sure you're getting lots of surface area covered on both sides so that the pick is clamped securely. It doesn't require a lot of grip to hold the pick firm if you're doing it right, but it can just fly out of your hand or move around a lot if you not holding it correctly.