1- Right of way: the surfer that catches a wave closest to its peak (the steepest part of the wave that is closest to the curling lip or otherwise breaking whitewater) has the right of way. So if two or more surfers are paddling for the same wave and heading in the same direction the surfer on the 'inside' usually has priority.
* If you drop into a wave in a crowded line-up, it's best to give a quick glance to make sure no one is behind you. If someone is in front of you then it's customary to alert them to get off your wave by shouting a loud-owl-like 'whooooo-oooooo'. Yelping 'heyyyyyyy' works fine too. My personal choice is the standard 'yyyyyhhheeeeeeeuuuu'. Just make sure its loud enough to hear and no matter what, if you call someone off a wave you had better commit to catching it. Nothing screams Kook Alert like hesitation.
2- Paddling Out: A surfer paddling out must always yield to the surfer riding a wave, even if that means taking a lip on the head or suffering a beat down from some soupy whitewash. If its clear you can scramble to the safety of the shoulder of an oncoming wave without jeopardizing the surfer's ride, then go for it. But the default move is to head straight for the inside of the wave towards the whitewash and let the surfer riding have the right of way to the shoulder. Nevertheless, its important to be as decisive and obvious as possible in which direction you are paddling to advise the surfer which path to take on the wave. There is nothing more frustrating then a paddling surfer ruining a wave for another by getting stuck in analysis paralysis. Pick a direction (preferably towards the inside of the wave) and stick to it.
3- Right or Left: When a wave breaks in both directions this is called an A-frame. To avoid confusion, call out in which direction you plan on going ahead of time. In other words, if you are paddling for the left, holler out "Going left' loud and clear. It's customary for surfers to 'split' waves when possible to allow one surfer to go right and the other left, and appreciated by everyone still waiting for a wave.
* Paddling Around: This important Code of Conduct is often ignored but equally important. Nothing irks a surfer more than getting 'snaked'. However, just as bothersome is the Paddle-Jockey. When entering a line-up or immediately after catching a wave its good practice to position yourself further towards the rear or side of the line-up. While it generally goes unspoken, wave priority is often based on who has been in position waiting the longest. Paddling around a group of surfers to position oneself closest to the peak is the equivalent of dropping-in to most surfers, and often the source of resentment against longboarders.