First, we will start with the basic knowledge of fishing: There is a bank close by. You may want to make a fire and cook the fish, because cooked fish will get you more Runescape money. Keep fishing to up the ranks.
It is better to be a member at this point. Unless you are only expect to raise your fishing level in your runescape account. You can reach Karamja at the Port Sarim Dock. If you are a member, it becomes easy when your level is 16. Heading towards Catherby and you can begin to fish for Mackerel when you get there.
Although quite a few of your fish will burn, the more you fish, cook, and bank, the less that your fish will get burning. Catherby has almost every type of fishing available. Be agreeable for those who are trying to level up by fishing.
Now, you have a lot of fish in hand. You could always teleport to Lumby, but that may take quite a long time to do, and it's all about fast RS gold-making. To save time, you can buy runescape accounts directly.