There are a variety of ways to generate or farm Gold within Runescape. The best way is to engage in the game to enjoy the activities that you decide to embark on. The most well-known strategies are:
Flipping trading on the Grand Exchange - always one of the best options to play any mmorpg game that has an international marketplace/exchange game. You must have RS Gold as your initial investment, and some experience to be able to make that happen.
Enchanting Sapphire Rings
Making Gold Rings
Making (smelting Iron bars, cooking Trouts and probably a several other lucrative items)
The Gathering (cutting Oak Trees, lumberjacking generally is my preferred choice)
Tanning Dragon hides
Additionally, you can find more information and details in the guide here.