Grinding is essentially a sideways surf on a green wave. The whole idea has come about with the development of flat planning hulls. Without one you will not be able to pull the move off.
Grinding a wave is an awesome feeling but your wave selection must also be right. Ideally the wave should be fast with a green face. The initiation of the grind is similar to that of a flat spin. Start with a reverse sweep (pry) until the boat has turned 90 degrees. When 90 degress is reached turn the reverse sweep into a forward stroke to steady the boat. At the same time drop your upstream edge so the hull is as flat on the wave a possible without power flipping. Keep your centre of gravity over the middle of the kayak and keep the grind going with subtle paddle strokes on your downstream side.