This is how I got my fishing up from level 1 to 40 in all of about 2 days.

-Shrimp (level 1-5)
raw-->cooked
These things are really annoying and you do not catch them too often. You have to have a net and i hope that your hands aren't sore now because they will be later. You can catch these outside of Al Kharid, SW of draynor village and S of port sarim

-Sardines(5-10)
raw-->cooked
I never actually knew about fishing sardines, so i caught shrimp till i was level 10, carpal tunnel here i come! If u want to catch sardines though, you're going to need a rod and some bait. wherever you can catch shrimp, you can catch sardines, just right click on bait

-Herring(10-15)
raw-->cooked
These are fairly easy to catch, when u fish for them, you'll probably end up catching more sardines then you will herrings but that will slowly start to change. Once again, rod and bait. You can catch these in the same spots as sardines and shrimp

-Anchovies(15-20)
raw-->cooked
Another fish that i didn't know about. I actually tried to throw my net into a fire once i discovered that i could catch sardines and herring. I had to go out and buy another net but it was worth it, anchovies are good, though u catch a lot of shrimp with them though. once again, same spot as shrimp, sardines and herring

-Trout(20-25)
raw-->cooked
My best friends, i love them (and no i do not have a trout fetish) This is the fish that got my fishing level up the most. It also got my cooking level up the most. These are easy to catch. You have to get a fly fishing rod and some feathers. u can find feathers at the farm north of Lumbridge these things are great to catch, easy too!You can catch these in rivers, outside Lumbridge and the barb village

-Pike(25-30)
raw-->cooked
These fish i hated. whenever i would try and catch them, i would catch either herring or sardines. i finally gave up on them and caught my trout again. If u want to catch them, u need a rod and some bait. You can find these in the same spot as trout, outside Lumbridge and barb village

-Salmon(30-35)
raw-->cooked
These fish are great, they are really easy to catch. they are also good to start to eat because they heal 9hp. and if you do not catch a salmon, you'll catch a trout which is still good. u need a fly fishing rod and some feathers. you can catch these in the same spot as tuna and salmon

-Tuna(35-40)
raw-->cooked
Your journey to level 40 fishing is almost over right? wrong! tuna are hard to catch. You have to stand there forever at the karamja docks with the little harpoon over your head waiting for 5 minutes to catch a fish, but by that time you have to move. to catch these you need a harpoon. you can catch these at karamja docks(take the boat from port sarim, do not forget to bring 6o gold, 30 each way)

-Lobster(40-45)
raw-->cooked
Your journey is finally over! you've finally reached level 40 fishing, your into the land of good food, lobster certs and sitting at karamja for hours on end catching them. Congrats!