What is the easiest/best way to make bells/money on Animal Crossing: New Leaf?

When you first get started, talk to Isabella and do what she asks until she gives you some fruit.

Do not sell this fruit. Instead get a shovel and plant it (equip the shovel, dig a hole, click on the fruit in inventory and "Bury 1"). Because the fruit Isabelle gave you is not native, it sells for much more than the standard fruit of your town.

Also be sure to plant (and save) the "perfect fruit" your town grows. These trees are temporary and will die after a few harvests, but you can make a lot of money off them until they do and the use one of the last fruit to replant it.

Finally buy a net and/or fishing pole and use them to catch fish and bugs. I would turn the initial example of each type into the museum, but any additional capture can be sold for decent bells.

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Your first goal, and the path to real money, is to get your initial house loan paid off. With enough fish,insects, and fruit you should be able to do this in the first day or two.

The next time you play after your home loan is paid off, the game will introduce Tortimer to you on the load screen. Find him in your town and talk to him. If you miss him you will have to pay off another loan before he will reappear. Tortimer will mention an island to you.

The next day you will gain access to a tropical island. It costs a 1,000 bells to go there, but the insects and fruit it has are all good sellers. (Import the fruit and plant it in your own village for some easy bells. Remember you can stack fruit.)

There are two important notes about the island. 1. You can only take things back you put in the chest at the end of the counter, and 2. the little girl will buy things off you for 5% Re-Tail's price, don't sell to her unless it is junk!

Outside you can talk to the statue next to the hut and borrow tools. The beetles that hang out on the tropical trees on the sand are worth a *lot* of bells when sold to Re-Tail, though most are hard to catch.

If you wait until after 7pm most of the day insects stop spawning, making the beetles more common. A shipping box full of these beetles can easily net you 400,000 bells or more, even without weeding out all the cheap ones.