Beginning riders typically start out at around 19-20 mph. That's a good speed to become familiar with the wakeboard while learning to control and maneuver it. This speed is also slow enough that you don't experience much drag, yet fast enough for you to practice cutting over the wake and moving into surface tricks.  As you improve and feel more confident, you can speed up to anywhere between 20-24 mph. A lot of this is dictated by your individual size, the boat's wake, rope length, and, of course, your comfort level.