Well, there are many ways to get money. There are several cheats all over the web, just google them. One is the fishing team cheat. All you have to do is hire the fishing team in the winter, and 1 million G is randomly awarded. This won't happen every time! Only once in a while. I've found that it usually works when I hire them for 3 days, but it works for 1 or 7 days as well.
Selling items: you can sell items to Van at the Inn when he comes on every day that ends in 3 or 8. (I think. I may be wrong on the dates... I don't pay attention...)
marriage: you have to pick someone you want to marry, and give them the items that they like. View all of their heart events (I can send these to you if you'd like. E-mail me if you want them at
[email protected] ), and DON'T LITTER! Really, don't drop anything outside your farm; the friend and affection points of everyone in the valley goes down very quickly.
shipping: the bin next to Takakura's house? stand in front of it (and facing it), put an item in your hands, and throw it in. Thomas will automatically come to collect shipments every day at 5pm.
Hope this helped!