The best way to get gold is to earn rs07 gp through the game. There are numerous methods for F2P and P2P money-making on YouTube as well as in the Runescape Wiki.
Personally, I have just crossed 10 million. One of my most favorite strategies include:
Cutting and selling yew wood 60 wood cutting (though this technique isn't as effective as it was in the past).
Mining Iron -- Very low-level requirement, and very fast, too. It's also the most efficient way to get mining training in F2P.
Smithing/Superheating runite bars -- This requires very high stats, but is the best method in F2P
High Level Alchemy Visit the wiki page on High Level alchemy market watch to locate the most valuable items.
Fletching arrows without heads It's quick and simple and with without any stat requirements. Simply purchase arrowshafts and feathers to flytch them, then return them to the seller to make a huge profit.
These methods are all F2P. There are additional methods listed on the Wiki as well as numerous more are available when you're already a member. Enjoy earning money and 2007 rs items in a safe and secure manner!