Draenor fish come in several sizes, and you can catch bigger fish with higher skill.
Draenor fish must be clicked to filet them for cooking reagents--you do not simply cook the fish.
In addition to pools, you can increase your chances of catching a particular fish with specific types of bait.
There are also new "social" fish, which can also be fished up in Draenor waters at low level like Awesomefish.
There are new items in WoD allowing you to increase your fishing skill temporarily like Tentacled Hat.
Fishing is also elaborately tied to your Garrison--you can recruit Nat Pagle, fish up special reward fish for him, and buy cool items like Reins of the Crimson Water Strider.
At level 3, you can fish up a Lunarfall Carp/ Frostdeep Minnow in your Garrison's water. Throwing it back into the water summons a Lunarfall Cavedweller/Frostdeep Cavedweller. This drops many cool items, including fishing hats, lures, fish, and bait.
Garrison building: Fishing Shack Level 3
Fishing 1 - 600
First, visit any trainer in the main cities of old Azeroth - just ask a guard, and learn Fishing Apprentice.
Go to the nearest water, find the fishing skill icon in your spell book. Stand in front of the lake/river and press the fishing button. Mouse over the lure in the water, and when it splashes, right click on it. Repeat this several hundred times.
Do not forget to visit your fishing trainer when you reach skill 75, 150, 225, 375, 450, and 525 !
That's it. You can fish anywhere, even in zones where your fishing skill is too low. You will mostly catch junk, but your fishing skill will increase if you catch something, it does not matter if it's a fish or some junk.