Just like irl you dont want to 'work' for $$$. Having fg allows you to take very favorable trades and 'gambles' when they rise. This is in general how to generate money from money in d2r. In real life you have something like S&P500
,cant have that here unless you want to take the higher risk of loaning someone with interest.
1) Crafting
If you're low on fg, you dont want to do amulets and rings because their variance is too high (you need massive rolls for acceptable profits). Sell all pgems and rals nstead to build capital.
2) Magic finding
Target worusk statues and latent sunder charms in NL. They do sell for a decent price. Again since you're still building capital, you want to sell the latent charms unrolled (same as above point)
When you have capital it's now up to your own strategy and risk tolerance to build from that.