It's mainly a low water shot fished from the skeers on the south side. The north side has some gullies but don't try to fish into the harbour from that side - it's quite dangerous.
On the skeers you can fish anywhere along them but there are 3 main shots - a top rock you can get on on a good tide flat skeers half way up the hole and a sticky up rock called the Beacon Rock 30 yards or so from the pier. Bigger the sea the better.
Hope that helps.