Fishing is a very popular and profitable skill that is used to heal life or hp. Fishing is best used in conjunction with cooking, as you can fish then cook and eat/sell your catch for a higher price. There are a few different kinds of fishing and they all need some sort of equipment. Fishing equipment may be bought from Port Sarim.
At the start, the only thing you can fish are shrimp. To catch these you need to buy a net. Shrimp is only found in saltwater, so they
cannot be caught in rivers. A good place to catch shrimp is the coastline south of Draynor Village. To fish, (left) click on the "fishing spot" in the water. Once caught they can be cooked in the usual ways.

Levels 1-15: Fish Shrimp at the fishing spots south of Draynor Village. Cook the fish as you go, then put them in your bank if you
wish to use them later, but don't hope to sell them, most players prefer to buy higher healing items.

Levels 20-40: Fish for trout and salmon (when you can catch them) to the east of barbarian village by the bridge. Cook your fish, then put them in your bank. Also if you wish you may catch Tuna with a harpoon at Karamja, although it is unlikely that you will progress much in levels.

Levels 40-50: Fish for lobsters at Karamja dock. Either cook them there, drop any burnt lobsters, and fish for more and cook those till you have a full load to take back to the bank in Draynor. If you are after experience and not so much the lobsters, you gain experience the fastest by fishing trout and salmon till around level 45, when you can catch lobsters faster.

Levels 50-99: Fish for swordfish at Karamja dock. When you are near full with just swordfish, cook them. Any you burn drop, and fish for some more until you get a full load of cooked swordfish to Draynor Bank. Some players prefer to continue fishing for lobsters until around level 60, when they can catch swordfish at a decent rate.