You have 2 choices,
- The mass gold farming (f2p)
and
- Small goldfarming
The mass one is literally creating 5-20 f2p accounts and doing something, Lobs in karamja seem to work best. others; smithing, tanning, wc.
The small goldfarming is getting members and doing higher stuff like fungus, dragons, hunter etc etc.
Try both and see which suites you better