I attached my gopro support on the nose of my plywood board, because it is the easier way to proceed (4 screws and voila).
Once the support is attached, you can clip the cam in both directions, so you can film the wave or your face.
It does the job, but I feel like on the video, the waves seem a little smaller than they are in real. On the other hand, as the cam is very close to the water you get the feeling of speed.
On this video of Jarret Liu, the cam seems to be attached to a stick he handles during the ride, I like the render, the angle constantly moves:https://www.youtube.com/watch?v=pNqK_6uTqgo