You can mow your grass and sell that as fodder, and you can also pick up all of the junk in your farm and in the town and sell it (rocks, weeds, etc) for 1G each. It's better than nothing if that's all you ahve right now.
You need to get a fishing rod too and then you can fish and sell them or eath them as well. You go to Galen/Nina's house on a Saturday around noon and then you will get a scene were Galen passes his old fishing rod onto you. Then it's fishing time!
I think this is about the best way to start. Chickens aren't a bad way to make money too. You have to show them lots of affection and then they produce better eggs. The cows are great source of income. Once you start producing things off the farm, just put it into the shipping box that Tanaka showed you and he'll take it off to market everyday and then he'll bring the gold to you.
Hope that helps.