Skilling up with Fishing really only requires that you head out to your favorite body of water with a fishing pole (preferably an unbreakable one like The Bone Rod or Brell's Fishin' Pole) and a ton of bait. If you don't have an unbreakable fishing pole, remember to bring extras with you as you head out to fish.
If you haven't managed to acquire a Fisherman's Companion yet, you can spend your time fishing in the Plane of Nightmare and the Plane of Valor to procure a supply of Nightmare Cichlid and Vallorian Discus. These can be be combined with Celandine Herb, Roots and a Filleting Knife to raise your fishing skill to 182 as well as using the bones to complete the quest for the Fisherman's Companion.
If you'd rather bypass standing around fishing for long periods of time and have access to a large quantity of foraged Roots, you can work on Prepared Fish made with Fresh Fish which can be purchased from Ramos Jerwan in the Plane of Knowledge. This will take your skill to 171.
To raise your skill from 183 to 200, you'll most likely just need to keep fishing. If you plan on taking your skill to 250 eventually, you'll want to move around a visit as many Fishing Holes as possible to obtain the fish you'll need to complete all the recipes needed to get to 250.
If you don't plan on raising your skill to 250, then you could consider fishing in The Overthere [RoS], Stratos, The Eastern Wastes [ToV], Cobalt Scar [CoV] or Maiden's Eye [ToL] to obtain the fish from any of those expansions and then using the subcombines to max your skill.