I know how it is. You've got a house to expand, public works to develop, stuff to buy—whatever your reason, you need bells, and you need bells bad. No worries. I'm here to help you make bank in New Leaf.
The Basic Stuff
When you start out—before you have the island unlocked—the best you can do is to rely on old-school methods. You'll want to make sure you bang every rock you come across with a shovel, because there's a daily money-spawning rock and a gemstone rock—as I mentioned in my original tips article. Sometimes you might even get a rock that spawns multiple gemstones instead of multiple bags of money, which is great. And, naturally, you'll want to search for fossils—these can fetch some decent bells, too.