Here is the easy way of making money/bells in Animal crossing : New Leaf.
Play with friends
It makes it easy to make money if you can visit other players's towns. You can sell items like fruits to other players.
Selling Perfect Fruits to other players
Your native fruits tree may grow a perfect fruits which will be worth more in the town where it's not the native fruit. The best thing to do is to plant a lot of them and sell it to other players.
If you have enough bells you can buy turnips from Joan on Sunday morning and then check with Reese to fins out about the Stalk Market price throughout the week. If the stock market goes up you can see them for a big profit and also you can see it to other players' town
Catch Fish and bugs on the Island
Visit resort island after 7pm to catch a lot of good value bugs and fish. Catch them and keep them in the box by Leilani's counter to send them back to your village and head to Reese to sell them for a profit.
Work in progress
Dig Up Fossils
Find the Money Rock
Find the "Fake" Rock to get Ore
Check the "High Price Item" at Re-Tail
Shoot Down Balloon Presents
Buy Fortune Cookies
Build a Police Station and Sell Items from the Lost and Found
Improve your Feng Shui
Wear Katrina's Good Luck Item