Try selling fish - that's my main sourse of money in the early game.
As you get your farming level up, you unlock crafting recipes for different machines - those are usually good for money, for example with mayonnaise machine you can make (shockingly) mayo, with preserves jars - pickles and jelly. The value of the last two depends on what crop you put in - cauliflower, melons, pumpkins already sell for alright money, so processing them is good for your wallet. Same thing with kegs - they take longer than preserves jars, but wine and juice typically sells for more.
Aside from farming, you can sell gems you find in the mines - won't bring you a fortune early, but that's usually a better use than hlard them. You can also plant a bunch of wild seeds, craft the harvest into more wild seeds and at the end of the season sell 'em all or make them into tea saplings which are still good for selling even after the nerf, though I don't do that often.
That's all I could think of for now, if you have any questions, feel free to ask.