Ok, to make LOTS of money you need to get the Fishing Rod.
You do not start off with it. In order to get it, you have to be good friends with Taro. Yes, why does it have to be the old balloon-head? To become friends with him you should just talk to him twice a day for the first 2 or 3 days then on day 4 you start giving him gifts. He likes things from your ranch. For all you people that are broke and canÃ¢Â€Â™t afford seeds to grow crops, stone material or wood material are also good. It is really important that you talk to him and give him gifts daily. As for any other villager in the game that you are befriending, if you ignore them for one day then when you go to give them a gift the next day they wonÃ¢Â€Â™t accept it! So you'll have to talk to them twice and the next day or two they'll take gifts from you again! Once Taro has 2000 FP you will wake up one day and Taro will be in front of your house with a fishing rod! You just catch as much fish as you can and ship em'. Then you'll be reelin' in the G's!
P.S. for all you girls if you catch and ship 50 fish Denny (a REALLY CUTE fisherman bachelor, who looks kind of like Kai from HMDS. Cute). Comes and lives on that big house on the beach! Happy Gaming!