I use the very common, minimal effort approach of filling the greenhouse with ancient fruit, filling a large shed with kegs, filling the cellar with casks, and making ancient fruit wine (aging as much of it as cellar throughput allows, which isn't all that much).
One could do a similar thing with starfruit, at the cost of significantly more effort. Likewise I know many people extend their ancient fruit planting outdoors, either on the farm or ideally on Ginger Island.
imnvs demonstrated that beehives work really nicely on the Island - year-round fairy rose honey. If you don't have the clock yet, a protective border of pathing would be prudent. I lost a beehive to weeds learning that one.
The most impressive and unhelpful answer to your question would probably be Shart's
Golden Egg Farm. (Unhelpful because by the time you can set this up by definition you no longer need money for anything).
I think the min-max folks make their money by going nuts in Skull Cavern and selling iridium bars. That couldn't be farther from my own playstyle so I don't pay too much attention though.
Ultimately though, making money in this game is a "You know what else works? Anything." situation. It's just a matter of how fast you earn it and how much effort it takes.
