Horde

Best place to start is in Bloodhoof Village in Mulgore.
Go speak to Harn Longcast and buy Brilliant Smallfish and Longjaw Mud Snapper recipes off of him. Now start fishing in Stonebull Lake.
Equip your rod and then apply the shiny bauble lure to it, as this will make catching fish easier.You'll want to catch about 60 Brilliant Smallfish and this should take about 40 minutes. You'll find that by the time you have caught 60 Brilliant Smallfish, you'll also have about 30 Longjaw Mud Snappers. Once you have 60, cook them. You can either build your own fire or jog back to Harn Longcast and use the fire in front of him. Cook the Brilliant Smallfish, then at level 50 start cooking Longjaw Mud Snappers (after learning the recipe you bought earlier).
You'll need to go and catch Longjaw Mud Snappers now and the best place for these is the pond in Orgrimmar by Lumark the Fishing trainer (I know you've been catching quite a few where you are, but the "drop rate" is a lot better in Orgrimmar).
Between levels 50 and 75 go learn journeyman fishing and cooking.
You'll now need to catch about 30 Longjaw Mud Snappers to get your cooking up to 100.
Now go to Tarren Mill in Hillsbrad and buy Bristle Whisker Catfish recipe off of Derak Nightfall.
Go to the river to the East of Tarren Mill and fish for Bristle Whisker Catfish. Depending on your cooking level, your going to need about 80-100 of these to get it up to 175.
Between levels 125 and 150 go learn expert cooking from trainer. You'll need to go to Booty Bay and buy a book for your Fishing level. Speak to Old Man Heming and buy the book Expert Fishing: The Bass and You.
Once your up to 175 cooking, go to Shadowprey Village in Desolace. Speak to Wulan and buy Mithril Head Trout recipe and start fishing on the pier there. Your going to need about 60 of these to get your cooking up to level 225.

At this point you should now have level 225 fishing and level 225 cooking. If your not level 35 yet, then this is as far as you can go. If you are level 35+ then you have two quests to complete before you can continue.

First quest: Cooking
Requirements: Level 35, 225 Cooking.

Go to Gadgetzan in Tanaris and speak to Dirge Quikcleave. He is in the tavern. He'll want you to bring him 12 Giant Eggs, 10 Zesty Clam Meat and 20 Alterac Swiss. You should actually be able to buy the eggs and clam meat off of AH, but in case you can't here's where to find them. Now according to the quest Giant Eggs drop off of Rocs in Tanaris or any large bird. The best place I found for the eggs, was the owlbeast in The Hinterlands. Only needed to kill about 20 of these to get my 12 eggs. They are about level 43 ish, so if your not that high a level, get help or wait till you can handle them. The clam meat comes from clams, naturally! Well to save you swimming around the sea looking for clams, your better off killing turtles at Steamwheedle Port or Raventusk Village. The drop rate is quite high and you'll have your clam meat in no time. The levels are 41 ish for Steamwheedle Port and 49-50 for Raventusk Village. The Alterac Swiss is the easiest part. Go to Hammerfall in Arathi Highlands and buy them off of the Inn Keeper. Hand them all in and you'll get your Artisan Cooking.