Making tons of money in Runscape can be time consuming. And you need the money to buy new stuff like weapons, armour and different things in the game. As you reach higher levels you will need more / better items and more gold, but you also make more money.
Chickens northwest of Lumbridge can be a good spot to make some gold. Chickens are very common. Kill all the chickens here and loot their feathers, if the chickens aren’t there wait for them to respawn. Loot everything from the chickens, but the feathers have the most value. When you’ve killed a bunch of chickens and looted their items. A chicken drops 5+ feathers each.
Once you are done, head back to a merchant in a town and sell everything to him. The feathers can fetch up to 7 gold each, more if you have a paying subscription. With the amount of feathers the chickens give you, you should be able to make some quick money this way.
Runescape money is also easily made while you are questing or grinding monsters. Try not to pay attention to how much loot/gold the mobs drop, this way you might get surprised when you head back to a merchant.
More powerful monsters drop more money, so try your luck on some and see how it goes. Don’t go up against something you cant kill though, this will only result in death which will delay your money making process. Monsters like giants are powerful but their loot can sell up to 400 gold each. Killing giants one of my favorite ways of making money in RS.