1. Understand the light before shooting
Has a surf photographer, you have to deal with tons of light sources and reflections.
The understanding of the way light is hitting the surface and the waves depending on the direction you are shooting and the time of the day will make you a better surf photographer.
To get the best quality photos, you want to shoot on an angle off the beach, in the direction where there is no reflection.
2. Bring the right lens
Focal length of 300 mm or 400 mm will make a big improvement in the quality of your pictures.
3. Take your shutter speed high!
Dynamic movement, water splashes… Lot of stuff move fast in surf photography. To capture the moment at its best, keep a shutter speed of 1/640 or above.
4. Shoot with a medium aperture
The benefit to a mid-range aperture is that you will have a bit more flexibility in your depth of field. That will allow the surfer to stay in focus for a way longer time and keep most of scene in focus.
5. Keep the ISO low
The lower your ISO, the less noise you will have in your final image. Since beach/surfing photography is generally going to have tons of available light, you should be able to keep your ISO at the very lowest setting.