The Rules

Here are two sites explaining, with pictures, who has right of way on a wave.

This one is in "black and white"

This site is also good, and provides a nice summary of the priority rules:

• Furthest Out or surfer that has been waiting longest
• Furthest Inside - closest surfer to the peak of the breaking wave
• First To Feet or first onto the wave has priority
• Communication - make a call, Left or Right