Just yesterday, after I-don't-remember-how-long of extensive fishing, I finally finished the Fisher King Queen achievement, and received the much underappreciated Master Angler title, as well as the hideous Slaughterfish Flesh Pink dye. It was a long journey to get there, and I now sigh in relief as I put away my fishing rods and arm myself once again to hunt the undead.
I learnt many things during this long stint, and I thought it would be a nice idea to share my experiences and suggestions for any other serious fishermen out there. These are mostly things I haven't found online anywhere else, so I won't be repeating what others have already said.
There are some really good fishing guides out there, so I suggest you go through them first (such as here and here). For map locations of different water types, I found Destinations to be a pretty useful addon, otherwise Esohead has some colour-coded maps that were also helpful. The Rare fish tracker addon is almost a must-have for more convenient fishing.
In no particular order:
Fishing in groups - Fishing in groups is useful only when you're starting out in a zone; this way you can rapidly get at least all the green fish. However, I would not recommend fishing with other people if you're looking for that last elusive blue fish, it's more likely to end up in your friends' bags, as I discovered more than once.
Fishing "cheer" - Related to the above point, apparently people around you can hear your character cheer when you catch a rare fish. So watch out for these cheers when you're fishing in groups and have had no luck!
Cyrodiil fishing - Honestly, I was dreading fishing in Cyrodiil, being completely dreadful at PvP (not to mention utterly relaxed due to all the fishing). But, it turned out to be surprisingly easy. Apart from the foul water fishes (which can be found all around Lake Rumare), all the fish showed up incredibly fast; I even got all three rare ocean fish from a single hole! So don't worry too much if you don't like PvP, fishing in Cyro is a breeze.
Fishing too long? - If you've been fishing for hours at an end in a zone without catching the last fish, just stop. This is a waste of good bait, and it's much easier to catch them if you return to the zone in a day or two.
Beyond all these little things, fishing is purely RNG-based. There are no patterns or tricks that might help you catch a particular type of fish faster. All you need is an endless supply of patience, bait, and possibly some good music or dance to keep you entertained!
Good luck and have fun fishing!
-Posted by Fisher Lariana (now officially retired)
P.S. A quick thanks to Arion for sending me an almost endless supply of slimy bugs and insects, couldn't have done it without him!
P.P.S. I still have a lot of bait left over, so if anyone in the guild wants to try their hand at fishing, let me know and I'll send it along!
Also the new harbourer of the Blood God, who gets kicked and punched everyday.