For more powerful waves try slipping off the board, holding the nose, with the cross section of the board held vertical. i.e if you are on the left side of the board, hold the right side up above the left side. It takes all the impact out of the wave. When you have the board flat it has the full width to collect the waves energy, but if the board is edge on it only has 2 1/2- 3 inches which is sweet F.A.
Your body is under the impact of the wave, so you take it on the shoulders and head.
If it is really powerful, turn around and face the beach, and sit on the tail.
If you are under the lip when it thumps ya, you need to rethink your approach.
If these don't work, throw the bugger and clean out the short boarders.